A030116 -id:A030116 - cp's OEIS frontend

A006356 a(n) = 2*a(n-1) + a(n-2) - a(n-3) for n >= 3, starting with a(0) = 1, a(1) = 3, and a(2) = 6.

1, 3, 6, 14, 31, 70, 157, 353, 793, 1782, 4004, 8997, 20216, 45425, 102069, 229347, 515338, 1157954, 2601899, 5846414, 13136773, 29518061, 66326481, 149034250, 334876920, 752461609, 1690765888, 3799116465, 8536537209, 19181424995

Offset: 0

N. J. A. Sloane

Number of distributive lattices; also number of paths with n turns when light is reflected from 3 glass plates.
Let u(k), v(k), w(k) be defined by u(1) = 1, v(1) = 0, w(1) = 0 and u(k+1) = u(k) + v(k) + w(k), v(k+1) = u(k) + v(k), w(k+1) = u(k); then {u(n)} = 1, 1, 3, 6, 14, 31, ... (this sequence with an extra initial 1), {v(n)} = 0, 1, 2, 5, 11, 25, ... (A006054 with its initial 0 deleted) and {w(n)} = {u(n)} prefixed by an extra 0 = A077998 with an extra initial 0. - Benoit Cloitre, Apr 05 2002
Also u(k)^2 + v(k)^2 + w(k)^2 = u(2*k). - Gary W. Adamson, Dec 23 2003
The n-th term of the series is the number of paths for a ray of light that enters two layers of glass and then is reflected exactly n times before leaving the layers of glass.
One such path (with 2 plates of glass and 3 reflections) might be:
...\........./..................
--------------------------------
....\/\..../....................
--------------------------------
........\/......................
--------------------------------
For a k-glass sequence, say a(n,k), a(n,k) is always asymptotic to z(k)*w(k)^n where w(k) = (1/2)/cos(k*Pi/(2*k+1)) and it is conjectured that z(k) is the root 1 < x < 2 of a polynomial of degree Phi(2k+1)/2.
Number of ternary sequences of length n-1 such that every pair of consecutive digits has a sum less than 3. That is to say, the pairs (1,2), (2,1) and (2,2) do not appear. - George J. Schaeffer (gschaeff(AT)andrew.cmu.edu), Sep 07 2004
Number of weakly up-down sequences of length n using the digits {1,2,3}. When n=2 the sequences are 11, 12, 13, 22, 23, 33.
Form the graph with matrix A = [1, 1, 1; 1, 0, 0; 1, 0, 1]. Then A006356 counts walks of length n that start at the degree 4 vertex. - Paul Barry, Oct 02 2004
In general, the g.f. for p glass plates is: A(x) = F_{p-1}(-x)/F_p(x) where F_p(x) = Sum_{k=0..p} (-1)^[(k+1)/2]*C([(p+k)/2],k)*x^k. - Paul D. Hanna, Feb 06 2006
Equals the INVERT transform of (1, 2, 1, 1, 1, ...) equivalent to a(n) = a(n-1) + 2*a(n-2) + a(n-3) + a(n-4) + ... + 1. a(6) = 70 = (31 + 2*14 + 6 + 3 + 1 + 1). - Gary W. Adamson, Apr 27 2009
a(n) = the number of terms in the n-th iterate of sequence A179542 generated from the rules a(0) = 1, then (1->1,2,3), (2->1,2), (3->1).
Example: 3rd iterate = (1,2,3,1,2,1,1,2,3,1,2,1,2,3) = 14 terms composed of a frequency of (6, 5, 3): (1's, 2's, and 3's), where a(3) = 14, and the [6, 5, 3] = top row and left column of the 3rd power of M, the matrix generator [1,1,1; 1,1,0; 1,0,0] or a(2) = 6, A006054(4) = 5, and a(1) = 3.
Given the heptagon diagonal lengths with edge = 1: (a = 1, b = 1.80193773..., c = 2.24697...) = (1, 2*cos(Pi/7), (1 + 2*cos(2*Pi/7))), and using the diagonal product formulas in [Steinbach], we obtain: c^n = c*a(n-2) + b*A006054(n) + a(n-3) corresponding to the top row of M^(n-1), in the case M^3 = [6, 5, 3]. Example: c^4 = 25.491566... = 6*c + 5*b + 3 = 13.481... + 9.00968... + 3. - Gary W. Adamson, Jul 18 2010
Equals row sums of triangle A180262. - Gary W. Adamson, Aug 21 2010
The number of the one-sided n-step prudent walks, avoiding 2 or more consecutive east steps. - Shanzhen Gao, Apr 27 2011
a(n) = [A_{7,2}^(n+2)](1,1), where A{7,2} is the 3 X 3 unit-primitive matrix (see [Jeffery]) A_{7,2} = [0,0,1; 0,1,1; 1,1,1]. The denominator of the generating function for this sequence is also the characteristic polynomial of A_{7,2}. - L. Edson Jeffery, Dec 06 2011 [See the comments for sequence A306334. - Petros Hadjicostas, Nov 17 2019]
a(n) is the top left entry of the n-th power of the 3 X 3 matrix [1, 1, 1; 1, 0, 0; 1, 0, 1] or of the 3 X 3 matrix [1, 1, 1; 1, 1, 0; 1, 0, 0]. - R. J. Mathar, Feb 03 2014
Successive sequences in this set (A006356, A006357, A006358, etc.) can be generated as follows: Begin with (1, 1, 1, 1, 1, 1, ...); and perform an operation with three steps to get the next sequence in the series. First, put alternate signs in the current series: With (1, 1, 1, ...) this equals (1, -1, 1, -1, ...); then take the inverse, getting (1, 1, 0, 0, 0, ...). Take the INVERT transform of the last step, getting (1, 2, 3, 5, 8, ...). Repeat the three steps using (1, 2, 3, 5, ...) --> (1, -2, 3, -5) --> (1, 2, 1, 1, 1, ...) --> (1, 3, 6, 14, 31, ...). Repeat the three steps using (1, 3, 6, 14, 31, ...), getting (1, 4, 10, 30, 85, ...) = A006357; and so on. - Gary W. Adamson, Aug 08 2019
Let W_n be the fence poset (a.k.a. zig-zag poset) of size n.  Let [2] be a chain of size 2.  Then a(n) is the number of antichains in the product poset W_n X [2]. See Berman- Koehler link. - Geoffrey Critzer, Jun 13 2023
a(n) is the number of double-dimer covers of the 2 X (n+1) square grid graph. See Musiker et al. link. - Nicholas Ovenhouse, Jan 07 2024
In general, the number of weakly up-down words of length n over an alphabet of size k is given by 4/(2*k+1)*|Sum_{j = 1..k} sin^2(2*j*Pi/(2*k+1))/(2*cos^2(2*j*Pi/(2*k+1)))^(n+1)| and the corresponding g. f. is given by V_(k-1)(-x/2)/W_k(x/2) if k is even and -W_(k-1)(-x/2) / V_k(x/2) if k is odd, where V_m(x) and W_m(x) are the Chebyshev polynomials of the third and fourth kind, respectively (see Paul D. Hanna's comment above and the Fried link). - Sela Fried, Apr 01 2025

J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124.
S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see p. 120).
R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, Reading, MA, 2nd edition, p. 291 (very briefly without generalizations).
J. Haubrich, Multinacci Rijen [Multinacci sequences], Euclides (Netherlands), Vol. 74, Issue 4, 1998, pp. 131-133.
Jay Kappraff, Beyond Measure, A Guided Tour Through Nature, Myth and Number, World Scientific, 2002.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..200
J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124. [Annotated scanned copy]
J. Berman and P. Köhler, On Dedekind Numbers and Two Sequences of Knuth, J. Int. Seq., Vol. 24 (2021), Article 21.10.7.
Sela Fried, A formula for the number of up-down words, arXiv:2503.02005 [math.CO], 2025.
Emma L. L. Gao, Sergey Kitaev, and Philip B. Zhang, Pattern-avoiding alternating words, arXiv:1505.04078 [math.CO], 2015.
Shanzhen Gao and Keh-Hsun Chen, Tackling Sequences From Prudent Self-Avoiding Walks, FCS'14, The 2014 International Conference on Foundations of Computer Science.
S. Gao and H. Niederhausen, Sequences Arising From Prudent Self-Avoiding Walks, 2010.
Manfred Goebel, Rewriting Techniques and Degree Bounds for Higher Order Symmetric Polynomials, Applicable Algebra in Engineering, Communication and Computing (AAECC), Volume 9, Issue 6 (1999), 559-573.
V. E. Hoggatt Jr. and M. Bicknell-Johnson, Reflections across two and three glass plates, Fibonacci Quarterly, volume 17 (1979), 118-142.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 451
L. E. Jeffery, Unit-primitive matrices
B. Junge and V. E. Hoggatt, Jr., Polynomials arising from reflections across multiple plates, Fib. Quart., 11 (1973), 285-291.
Peter Köhler, The Central Decomposition of FD_01(n), Order (2021).
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30.
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. (Annotated scanned copy)
Julien Leroy, Michel Rigo, and Manon Stipulanti, Behavior of Digital Sequences Through Exotic Numeration Systems, Electronic Journal of Combinatorics 24(1) (2017), #P1.44.
Leo Moser, Problem B-6: some reflections, Fib. Quart. Vol. 1, No. 4 (1963), 75-76.
Leo Moser and Max Wyman, Multiple reflections, Fib. Quart., 11 (1973).
Gregg Musiker, Ralf Schiffler, Nicholas Ovenhouse, and Sylvester Zhang, Higher Dimer Covers on Snake Graphs, arXiv:2306.14389 [math.CO], 2023.
Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992.
Lingjuan Shi and Kai Deng, The Numbers of Perfect and Maximal Matchings in Double Hexagonal Chains, Match Comm. Math. Comp. Chem. (2025) 659-685. See p. 8.
P. Steinbach, Golden fields: a case for the heptagon, Math. Mag. 70 (1997), no. 1, 22-31.
R. Witula, D. Slota and A. Warzynski, Quasi-Fibonacci Numbers of the Seventh Order, J. Integer Seq., 9 (2006), Article 06.4.3.
Index entries for linear recurrences with constant coefficients, signature (2,1,-1).

Cf. A000217, A000330, A050446, A050447, A006054, A077998, A052534, A052994, A052949.
See also A006357-A006359, A025030, A030112-A030116.
Cf. A038196 (3-wave sequence).
Cf. A179542. - Gary W. Adamson, Jul 18 2010
Cf. A180262. - Gary W. Adamson, Aug 21 2010
Cf. A033303, A190360, A306334.

a006056 n = a006056_list !! n
a006056_list = 1 : 3 : 6 : zipWith (+) (map (2 *) $ drop 2 a006056_list)
   (zipWith (-) (tail a006056_list) a006056_list)
-- Reinhard Zumkeller, Oct 14 2011

[ n eq 1 select 1 else n eq 2 select 3 else n eq 3 select 6 else 2*Self(n-1)+Self(n-2)- Self(n-3): n in [1..40] ] ; // Vincenzo Librandi, Aug 20 2011

A006356:=-(-1-z+z**2)/(1-2*z-z**2+z**3); # conjectured by Simon Plouffe in his 1992 dissertation

LinearRecurrence[{2,1,-1},{1,3,6},30] (* or *) CoefficientList[ Series[ (1+x-x^2)/(1-2x-x^2+x^3),{x,0,30}],x] (* Harvey P. Dale, Jul 06 2011 *)
Table[If[n==0, a2=0; a1=1; a0=1, a3=a2; a2=a1; a1=a0; a0=2*a1+a2-a3], {n, 0, 29}] (* Jean-François Alcover, Apr 30 2013 *)

a(n):=sum(sum((sum(binomial(j,-3*k+2*j+i)*(-1)^(j-k)*binomial(k,j),j,0,k))*binomial(n+k-i-1,k-1),i,k,n),k,1,n); /* Vladimir Kruchinin, May 05 2011 */

{a(n)=local(p=3);polcoeff(sum(k=0,p-1,(-1)^((k+1)\2)*binomial((p+k-1)\2,k)* (-x)^k)/sum(k=0,p,(-1)^((k+1)\2)*binomial((p+k)\2,k)*x^k+x*O(x^n)),n)} \\ Paul D. Hanna, Feb 06 2006

Vec((1+x-x^2)/(1-2*x-x^2+x^3)+O(x^66)) \\ Joerg Arndt, Apr 30 2013

from math import comb
def A006356(n): return sum(comb(j,a)*comb(k,j)*comb(n+k-i,k-1)*(-1 if j-k&1 else 1) for k in range(1,n+2) for i in range(k,n+2) for j in range(k+1) if (a:=-3*k+2*j+i)>=0) # Chai Wah Wu, Feb 19 2024

a(n) is asymptotic to z(3)*w(3)^n where w(3) = (1/2)/cos(3*Pi/7) and z(3) is the root 1 < X < 2 of P(3, X) = 1 - 14*X - 49*X^2 + 49*X^3. w(3) = 2.2469796.... z(3) = 1.220410935...
G.f.: (1 + x - x^2)/(1 - 2*x - x^2 + x^3). - Paul D. Hanna, Feb 06 2006
a(n) = a(n-1) + a(n-2) + A006054(n+1). - Gary W. Adamson, Jun 05 2008
a(n) = A006054(n+2) + A006054(n+1) - A006054(n). - R. J. Mathar, Apr 07 2011
a(n-1) = Sum_{k = 1..n} Sum_{i = k..n} Sum_{j = 0..k} binomial(j, -3*k+2*j+i) * (-1)^(j-k) * binomial(k, j) * binomial(n+k-i-1, k-1). - Vladimir Kruchinin, May 05 2011
Sum_{k=0..n} a(k) = a(n+1) - a(n-1) - 1. - Greg Dresden and Mina BH Arsanious, Aug 23 2023

Recurrence, alternative description from Jacques Haubrich (jhaubrich(AT)freeler.nl)

Alternative definition added by Andrew Niedermaier, Nov 11 2008

A006359 Number of distributive lattices; also number of paths with n turns when light is reflected from 6 glass plates.

Original entry on oeis.org

1, 6, 21, 91, 371, 1547, 6405, 26585, 110254, 457379, 1897214, 7869927, 32645269, 135416457, 561722840, 2330091144, 9665485440, 40093544735, 166312629795, 689883899612, 2861717685450, 11870733787751, 49241167758705, 204258021937291, 847285745315256

Offset: 0

N. J. A. Sloane

Let M denotes the 6 X 6 matrix = row by row (1,1,1,1,1,1)(1,1,1,1,1,0)(1,1,1,1,0,0)(1,1,1,0,0,0)(1,1,0,0,0,0)(1,0,0,0,0,0) and A(n) the vector (x(n),y(n),z(n),t(n),u(n),v(n)) = M^n*A where A is the vector (1,1,1,1,1,1) then a(n) = x(n). - Benoit Cloitre, Apr 02 2002

J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124.
Manfred Goebel, Rewriting Techniques and Degree Bounds for Higher Order Symmetric Polynomials, Applicable Algebra in Engineering, Communication and Computing (AAECC), Volume 9, Issue 6 (1999), 559-573.
J. Haubrich, Multinacci Rijen [Multinacci sequences], Euclides (Netherlands), Vol. 74, Issue 4, 1998, pp. 131-133.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..200
J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124. [Annotated scanned copy]
Emma L. L. Gao, Sergey Kitaev, and Philip B. Zhang, Pattern-avoiding alternating words, arXiv:1505.04078 [math.CO], 2015.
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30.
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. (Annotated scanned copy)
Index entries for linear recurrences with constant coefficients, signature (3,6,-4,-5,1,1).

Cf. A000217, A000330, A050446, A050447, A006356, A006357, A006358.

See also A025030, A030112, A030113, A030114, A030115, A030116.

A=seq(a.j,j=0..5):grammar1:=[Q5,{ seq(Q.i=Union(Epsilon,seq(Prod(a.j,Q.j),j=5-i..5)),i=0..5), seq(a.j=Z,j=0..5) }, unlabeled]: seq(count(grammar1,size=j),j=0..22); # Zerinvary Lajos, Mar 09 2007

LinearRecurrence[{3,6,-4,-5,1,1},{1,6,21,91,371,1547},30] (* Harvey P. Dale, Sep 03 2016 *)

k=5; M(k)=matrix(k,k,i,j,if(1-sign(i+j-k),0,1)); v(k)=vector(k,i,1); a(n)=vecmax(v(k)*M(k)^n)

{a(n)=local(p=6);polcoeff(sum(k=0,p-1,(-1)^((k+1)\2)*binomial((p+k-1)\2,k)* (-x)^k)/sum(k=0,p,(-1)^((k+1)\2)*binomial((p+k)\2,k)*x^k+x*O(x^n)),n)} \\ Paul D. Hanna, Feb 06 2006

G.f.: -(z^4 + z^3 - 3z^2 - 2z + 1) / (-1 + 3z + 6z^2 - 4z^3 - 5z^4 + z^5 + z^6). - M. Goebel (manfredg(AT)ICSI.Berkeley.EDU) Jul 26 1997
a(n) = 3*a(n-1) + 6*a(n-2) - 4*a(n-3) - 5*a(n-4) + a(n-5) + a(n-6).
a(n) is asymptotic to z(6)*w(6)^n where w(6) = (1/2)/cos(6*Pi/13) and z(6) is the root 1 < x < 2 of P(6, X) = -1 - 91*X + 2366*X^2 + 26364*X^3 - 142805*X^4 - 371293*X^5 + 371293*X^6 - Benoit Cloitre, Oct 16 2002
G.f.: A(x) = (1 + 3*x - 3*x^2 - 4*x^3 + x^4 + x^5)/(1 - 3*x - 6*x^2 + 4*x^3 + 5*x^4 - x^5 - x^6). - Paul D. Hanna, Feb 06 2006
G.f.: 1/(-x-1/(-x-1/(-x-1/(-x-1/(-x-1/(-x-1)))))). - Paul Barry, Mar 24 2010

Alternative description from Jacques Haubrich (jhaubrich(AT)freeler.nl)

More terms from James Sellers, Dec 24 1999

A006357 Number of distributive lattices; also number of paths with n turns when light is reflected from 4 glass plates.

Original entry on oeis.org

1, 4, 10, 30, 85, 246, 707, 2037, 5864, 16886, 48620, 139997, 403104, 1160693, 3342081, 9623140, 27708726, 79784098, 229729153, 661478734, 1904652103, 5484227157, 15791202736, 45468956106, 130922641160, 376976720745, 1085461206128, 3125460977225

Offset: 0

N. J. A. Sloane

Let M denotes the 4 X 4 matrix = row by row (1,1,1,1)(1,1,1,0)(1,1,0,0)(1,0,0,0) and A(n) the vector (x(n),y(n),z(n),t(n))=M^n*A where A is the vector (1,1,1,1) then a(n)=x(n). - Benoit Cloitre, Apr 02 2002
In general, the g.f. for p glass plates is A(x) = F_{p-1}(-x)/F_p(x) where F_p(x) = Sum_{k=0,p} (-1)^[(k+1)/2]*C([(p+k)/2],k)*x^k. - Paul D. Hanna, Feb 06 2006
a(n)/a(n-1) tends to 2.879385..., the longest diagonal of a nonagon with edge 1; or: sin(4*Pi/9)/sin(Pi/9). The sequence is the INVERT transform of (1, 3, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...). - Gary W. Adamson, Jul 16 2015

J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124.
S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see p. 120).
J. Haubrich, Multinacci Rijen [Multinacci sequences], Euclides (Netherlands), Vol. 74, Issue 4, 1998, pp. 131-133.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..200
J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124. [Annotated scanned copy]
Emma L. L. Gao, Sergey Kitaev, and Philip B. Zhang, Pattern-avoiding alternating words, arXiv:1505.04078 [math.CO], 2015.
Manfred Goebel, Rewriting Techniques and Degree Bounds for Higher Order Symmetric Polynomials, Applicable Algebra in Engineering, Communication and Computing (AAECC), Volume 9, Issue 6 (1999), 559-573.
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30.
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. (Annotated scanned copy)
Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992
Index entries for linear recurrences with constant coefficients, signature (2,3,-1,-1).

Cf. A000217, A000330, A050446, A050447, A006356-A006359, A025030, A030112-A030116, A122167, A091024.

Cf. A038197 (4-wave sequence).

LinearRecurrence[{2,3,-1,-1},{1,4,10,30},30] (* Harvey P. Dale, Nov 18 2013 *)

a(n)=local(p=4);polcoeff(sum(k=0,p-1,(-1)^((k+1)\2)*binomial((p+k-1)\2,k)* (-x)^k)/sum(k=0,p,(-1)^((k+1)\2)*binomial((p+k)\2,k)*x^k+x*O(x^n)),n) \\ Paul D. Hanna

G.f.: (1 + 2*x - x^2 - x^3)/( (1 +x)*(1 -3*x +x^3) ). - Simon Plouffe in his 1992 dissertation
a(n) = 2*a(n-1) + 3*a(n-2) - a(n-3) - a(n-4).
a(n) is asymptotic to z(4)*w(4)^n where w(4) = (1/2)/cos(4*Pi/9) and z(4) is the root 1 < x < 2 of P(4, X) = 1 + 27*X - 324*X^2 + 243*X^3. - Benoit Cloitre, Oct 16 2002
Binomial transform of A122167(unsigned): (1, 3, 3, 11, 10, 40, 33, 146, ...). - Gary W. Adamson, Nov 24 2007
G.f.: 1/(-x-1/(-x-1/(-x-1/(-x-1)))). - Paul Barry, Mar 24 2010

Recurrence, alternative description from Jacques Haubrich (jhaubrich(AT)freeler.nl)
More terms from James Sellers, Dec 24 1999
More terms from Paul D. Hanna, Feb 06 2006

A006358 Number of distributive lattices; also number of paths with n turns when light is reflected from 5 glass plates.

Original entry on oeis.org

1, 5, 15, 55, 190, 671, 2353, 8272, 29056, 102091, 358671, 1260143, 4427294, 15554592, 54648506, 191998646, 674555937, 2369942427, 8326406594, 29253473175, 102777312308, 361091343583, 1268635610806, 4457144547354

Offset: 0

N. J. A. Sloane

Let M denotes the 5 X 5 matrix = row by row (1,1,1,1,1)(1,1,1,1,0)(1,1,1,0,0)(1,1,0,0,0)(1,0,0,0,0) and A(n) the vector (x(n),y(n),z(n),t(n),u(n)) = M^n*A where A is the vector (1,1,1,1,1); then a(n)=y(n). - Benoit Cloitre, Apr 02 2002

J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124.
S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see p. 120).
J. Haubrich, Multinacci Rijen [Multinacci sequences], Euclides (Netherlands), Vol. 74, Issue 4, 1998, pp. 131-133.
D. E. Knuth, Art of Computer Programming, Vol. 3, Sect. 5.4.3, Column T1.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..200
J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124. [Annotated scanned copy]
Emma L. L. Gao, Sergey Kitaev, and Philip B. Zhang, Pattern-avoiding alternating words, arXiv:1505.04078 [math.CO], 2015.
Manfred Goebel, Rewriting Techniques and Degree Bounds for Higher Order Symmetric Polynomials, Applicable Algebra in Engineering, Communication and Computing (AAECC), Volume 9, Issue 6 (1999), 559-573.
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30.
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. (Annotated scanned copy)
Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992
Index entries for linear recurrences with constant coefficients, signature (3,3,-4,-1,1).

Cf. A000217, A000330, A050446, A050447.
See also A006356-A006359, A025030, A030112-A030116.
Cf. A038201 (5-wave sequence).

A=seq(a.j,j=0..4):grammar1:=[Q4,{ seq(Q.i=Union(Epsilon,seq(Prod(a.j,Q.j),j=4-i..4)),i=0..4), seq(a.j=Z,j=0..4) }, unlabeled]: seq(count(grammar1,size=j),j=0..23); # Zerinvary Lajos, Mar 09 2007
A006358:=-(z-1)*(z**3-3*z-1)/(-1+3*z+3*z**2-4*z**3-z**4+z**5); # conjectured by Simon Plouffe in his 1992 dissertation

m = Table[ If[j <= 6-i, 1, 0], {i, 1, 5}, {j, 1, 5}] ; a[n_] := MatrixPower[m, n].Table[1, {5}]; Table[ a[n], {n, 0, 23}][[All, 1]] (* Jean-François Alcover, Dec 08 2011, after Benoit Cloitre *)
LinearRecurrence[{3,3,-4,-1,1},{1,5,15,55,190},30] (* Harvey P. Dale, Jun 16 2016 *)

k=5; M(k)=matrix(k,k,i,j,if(1-sign(i+j-k),0,1)); v(k)=vector(k,i,1); a(n)=vecmax(v(k)*M(k)^n)

{a(n)=local(p=5);polcoeff(sum(k=0,p-1,(-1)^((k+1)\2)*binomial((p+k-1)\2,k)* (-x)^k)/sum(k=0,p,(-1)^((k+1)\2)*binomial((p+k)\2,k)*x^k+x*O(x^n)),n)}

a(n) = 3*a(n-1) + 3*a(n-2) - 4*a(n-3) - a(n-4) + a(n-5).
a(n) is asymptotic to z(5)*w(5)^n where w(5) = (1/2)/cos(5*Pi/11) and z(5) is the root 1 < x < 2 of P(5, X) = -1 + 55*X + 847*X^2 - 5324*X^3 - 14641*X^4 + 14641*X^5. - Benoit Cloitre, Oct 16 2002
G.f.: A(x) = (1 + 2*x - 3*x^2 - x^3 + x^4)/(1 - 3*x - 3*x^2 + 4*x^3 + x^4 - x^5). - Paul D. Hanna, Feb 06 2006

Alternative description and formula from Jacques Haubrich (jhaubrich(AT)freeler.nl)

More terms from James Sellers, Dec 24 1999

A025030 Number of distributive lattices; also number of paths with n turns when light is reflected from 7 glass plates.

Original entry on oeis.org

1, 7, 28, 140, 658, 3164, 15106, 72302, 345775, 1654092, 7911970, 37846314, 181033035, 865951710, 4142180085, 19813648817, 94776329265, 453351783116, 2168556616440, 10373043626906, 49618272850056, 237343357526002

Offset: 0

Jacques Haubrich (jhaubrich(AT)freeler.nl)

Let M(7) be the 7 X 7 matrix: (0,0,0,0,0,0,1)/(0,0,0,0,0,1,1)/(0,0,0,0,1,1,1)/(0,0,0,1,1,1,1)/(0,0,1,1,1,1,1)/(0,1,1,1,1,1,1)/(1,1,1,1,1,1,1) and let v(7) be the vector (1,1,1,1,1,1,1); then v(7)*M(7)^n = (x,y,z,t,u,v,a(n)). - Benoit Cloitre, Sep 29 2002

J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124.
J. Haubrich, Multinacci Rijen [Multinacci sequences], Euclides (Netherlands), Vol. 74, Issue 4, 1998, pp. 131-133.

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124. [Annotated scanned copy]
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30.
Index entries for linear recurrences with constant coefficients, signature (4,6,-10,-5,6,1,-1).

See also A006356-A006359, A030112-A030116.

I:=[1, 7, 28, 140, 658, 3164, 15106]; [n le 7 select I[n] else 4*Self(n-1)+6*Self(n-2)-10*Self(n-3)-5*Self(n-4)+6*Self(n-5)+Self(n-6)-Self(n-7): n in [1..30]]; // Vincenzo Librandi, Apr 22 2012

CoefficientList[Series[(1+3*x-6*x^2-4*x^3+5*x^4+x^5-x^6)/((1-x)*(1+x-x^2)*(1-4*x-4*x^2+x^3+x^4)),{x,0,30}],x] (* Vincenzo Librandi, Apr 22 2012 *)
LinearRecurrence[{4,6,-10,-5,6,1,-1},{1,7,28,140,658,3164,15106},30] (* Harvey P. Dale, Feb 26 2023 *)

k=7; M(k)=matrix(k,k,i,j,if(1-sign(i+j-k),0,1)); v(k)=vector(k,i,1); a(n)=vecmax(v(k)*M(k)^n)

a(n) = 4*a(n-1) + 6*a(n-2) - 10*a(n-3) - 5*a(n-4) + 6*a(n-5) + a(n-6) - a(n-7).
a(n) is asymptotic to z(7)*w(7)^n where w(7) = (1/2)/cos(7*Pi/15) and z(7) is the root 1 < x < 2 of P(7, X) = 1 - 120*X - 8100*X^2 - 57375*X^3 + 50625*X^4. - Benoit Cloitre, Oct 16 2002
G.f.: (1 + 3*x - 6*x^2 - 4*x^3 + 5*x^4 + x^5 - x^6)/((1 - x)*(1 + x - x^2)*(1 - 4*x - 4*x^2 + x^3 + x^4)). - Colin Barker, Mar 31 2012

More terms from Benoit Cloitre, Sep 29 2002

A030112 Number of distributive lattices; also number of paths with n turns when light is reflected from 8 glass plates.

Original entry on oeis.org

1, 8, 36, 204, 1086, 5916, 31998, 173502, 940005, 5094220, 27604798, 149590922, 810627389, 4392774126, 23804329059, 128995094597, 699021261776, 3787979292364, 20526967746120, 111235140046330, 602780523265720, 3266453022809170, 17700829632401740, 95920366069513405

Offset: 0

Jacques Haubrich (jhaubrich(AT)freeler.nl)

Let M(8) be the 8 X 8 matrix (0,0,0,0,0,0,0,1)/(0,0,0,0,0,0,1,1)/(0,0,0,0,0,1,1,1)/(0,0,0,0,1,1,1,1)/(0,0,0,1,1,1,1,1)/(0,0,1,1,1,1,1,1)/(0,1,1,1,1,1,1,1)/(1,1,1,1,1,1,1,1) and let v(8) be the vector (1,1,1,1,1,1,1,1); then v(8)*M(8)^n = (x,y,z,t,u,v, w,a(n)). - Benoit Cloitre, Sep 29 2002

For a k-glass sequence, say a(n,k), a(n,k) is always asymptotic to z(k)*w(k)^n where w(k)=(1/2)/cos(k*Pi/(2k+1)) and it is conjectured that z(k) is the root 1Benoit Cloitre, Oct 16 2002

J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124.
J. Haubrich, Multinacci Rijen [Multinacci sequences], Euclides (Netherlands), Vol. 74, Issue 4, 1998, pp. 131-133.

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
J. Berman and P. Koehler, Cardinalities of finite distributive lattices, Mitteilungen aus dem Mathematischen Seminar Giessen, 121 (1976), 103-124. [Annotated scanned copy]
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30.
Index entries for linear recurrences with constant coefficients, signature (4,10,-10,-15,6,7,-1,-1).

See also A006356-A006359, A025030, A030113-A030116.

I:=[1, 8, 36, 204, 1086, 5916, 31998, 173502]; [n le 8 select I[n] else 4*Self(n-1)+10*Self(n-2)-10*Self(n-3)-15*Self(n-4)+6*Self(n-5)+7*Self(n-6)-Self(n-7)-Self(n-8):  n in [1..25]]; // Vincenzo Librandi, Apr 22 2012

nmax:=20: with(LinearAlgebra): M:=Matrix([[0,0,0,0,0,0,0,1], [0,0,0,0,0,0,1,1], [0,0,0,0,0,1,1,1], [0,0,0,0,1,1,1,1], [0,0,0,1,1,1,1,1], [0,0,1,1,1,1,1,1], [0,1,1,1,1,1,1,1], [1,1,1,1,1,1,1,1]]): v:= Vector[row]([1,1,1,1,1,1,1,1]): for n from 0 to nmax do b:=evalm(v&*M^n): a(n):=b[8] od: seq(a(n), n=0..nmax); # Johannes W. Meijer, Aug 03 2011

CoefficientList[Series[(1+x)*(1-x-x^2)*(1+4*x-4*x^2-x^3+x^4)/(1-4*x-10*x^2+10*x^3+15*x^4-6*x^5-7*x^6+x^7+x^8),{x,0,30}],x] (* Vincenzo Librandi, Apr 22 2012 *)

k=8; M(k)=matrix(k,k,i,j,if(1-sign(i+j-k),0,1)); v(k)=vector(k,i,1); a(n)=vecmax(v(k)*M(k)^n)

a(n) = 4*a(n-1)+ 10*a(n-2)-10*a(n-3)-15*a(n-4)+ 6*a(n-5)+7*a(n-6)-a(n-7)-a(n-8). - Benoit Cloitre, Oct 09 2002
a(n) is asymptotic to z(8)*w(8)^n where w(8)=(1/2)/cos(8*Pi/17) and z(8) is the root 1Benoit Cloitre, Oct 16 2002
G.f.: (1+x)*(1-x-x^2)*(1+4*x-4*x^2-x^3+x^4)/(1-4*x-10*x^2+10*x^3+15*x^4-6*x^5-7*x^6+x^7+x^8). - Colin Barker, Mar 31 2012

More terms from Benoit Cloitre, Sep 29 2002

Comment corrected by Johannes W. Meijer, Aug 03 2011

cp's OEIS Frontend

A006356 a(n) = 2*a(n-1) + a(n-2) - a(n-3) for n >= 3, starting with a(0) = 1, a(1) = 3, and a(2) = 6.

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A006359 Number of distributive lattices; also number of paths with n turns when light is reflected from 6 glass plates.

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A006357 Number of distributive lattices; also number of paths with n turns when light is reflected from 4 glass plates.

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A006358 Number of distributive lattices; also number of paths with n turns when light is reflected from 5 glass plates.

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A025030 Number of distributive lattices; also number of paths with n turns when light is reflected from 7 glass plates.

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A030112 Number of distributive lattices; also number of paths with n turns when light is reflected from 8 glass plates.

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