cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A024537 a(n) = floor( a(n-1)/(sqrt(2) - 1) ), with a(0) = 1.

Original entry on oeis.org

1, 2, 4, 9, 21, 50, 120, 289, 697, 1682, 4060, 9801, 23661, 57122, 137904, 332929, 803761, 1940450, 4684660, 11309769, 27304197, 65918162, 159140520, 384199201, 927538921, 2239277042, 5406093004, 13051463049, 31509019101, 76069501250, 183648021600
Offset: 0

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Author

Keywords

Comments

a(n) = A048739(n-1)+1 = 1/2 * (P(n)+P(n-1)+1), with P(n) = Pell numbers (A000129).
Number of (3412,#)-avoiding involutions in S_{n+1}, where # can be one of 22 patterns, see Egge reference.
Number of (s(0), s(1), ..., s(n+1)) such that 0 < s(i) < 4 and |s(i) - s(i-1)| <= 1 for i = 1,2,...,n+1, s(0) = 1, s(n+1) = 1. - Herbert Kociemba, Jun 02 2004
Define the sequence S(a_0,a_1) by a_{n+2} is the least integer such that a_{n+2}/a_{n+1} > a_{n+1}/a_n for n >= 0 . This is S(2,4). (For proof, see the Alekseyev link.) - R. K. Guy
This sequence occurs in the lower bound of the order of the set of equivalent resistances of n equal resistors combined in series and in parallel (A048211). - Sameen Ahmed Khan, Jun 28 2010
Partial sums of the Pell numbers prefaced with a 1: (1, 1, 2, 5, 12, 29, 70, ...). - Gary W. Adamson, Feb 15 2012
The number of ways to write an n-bit binary sequence and then give runs of ones weakly incrementing labels starting with 1, e.g., 0011010011022203003330044040055555. - Andrew Woods, Jan 03 2015
Sums of the positive coefficients in Chebyshev polynomials of the first kind, beginning with T_1. a(n+1)/a(n) approaches 1/(sqrt(2)-1). - Gregory Gerard Wojnar, Mar 19 2018

Crossrefs

Programs

  • Mathematica
    NestList[Floor[#/(Sqrt[2]-1)]&,1,40] (* Harvey P. Dale, Apr 01 2012 *)
    LinearRecurrence[{3, -1, -1}, {1, 2, 4}, 31] (* Jean-François Alcover, Jan 07 2019 *)
  • PARI
    a=vector(99);a[1]=1; for(n=2,#a,a[n]=a[n-1]\(sqrt(2) - 1)); a \\ Charles R Greathouse IV, Jun 14 2011
    
  • PARI
    x='x+O('x^99); Vec((1-x-x^2)/((1-x)*(1-2*x-x^2))) \\ Altug Alkan, Mar 19 2018

Formula

a(n) = 2*a(n-1) + a(n-2) - 1. - Christian G. Bower
a(n) = 3*a(n-1) - a(n-2) - a(n-3).
From Paul Barry, Dec 25 2003: (Start)
G.f.: (1 - x - x^2)/((1-x)*(1 - 2*x - x^2)) = (1 - x - x^2)/(1 - 3*x + x^2 + x^3).
E.g.f.: exp((1+sqrt(2))*x)*(1+sqrt(2))/4+exp((1-sqrt(2))*x)*(1-sqrt(2))/4+exp(x)/2. (End)
a(n) = (1/4)*(2 + (1-sqrt(2))^(n+1) + (1+sqrt(2))^(n+1)). - Herbert Kociemba, Jun 02 2004
Let M = a tridiagonal matrix with all 1's in the super and main diagonals and [1,1,0,0,0,...] in the subdiagonal, and let V = vector [1,0,0,0,...], and the rest zeros. The sequence is generated as the leftmost column from iterates of M*V. - Gary W. Adamson, Jun 07 2011
G.f.: (1 + Q(0)*x/2)/(1-x), where Q(k) = 1 + 1/(1 - x*(4*k+2 + x)/( x*(4*k+4 + x) + 1/Q(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Sep 06 2013
a(n) = A171842(n+1), n>=0. That sequence starts with an extra 1. - Andrew Woods, Jan 03 2015
a(n) = 1 + sum_{k=1..floor((n+1)/2)} C(n+1,2*k)*2^(k-1). - Andrew Woods, Jan 03 2015

Extensions

Edited by N. J. A. Sloane at the suggestion of Max Alekseyev, Aug 24 2007

A034182 Number of not-necessarily-symmetric n X 2 crossword puzzle grids.

Original entry on oeis.org

1, 5, 15, 39, 97, 237, 575, 1391, 3361, 8117, 19599, 47319, 114241, 275805, 665855, 1607519, 3880897, 9369317, 22619535, 54608391, 131836321, 318281037, 768398399, 1855077839, 4478554081, 10812186005, 26102926095, 63018038199, 152139002497, 367296043197
Offset: 1

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Author

Keywords

Comments

n X 2 binary arrays with a path of adjacent 1's and no path of adjacent 0's from top row to bottom row. - R. H. Hardin, Mar 21 2002
Define a triangle with T(n,1) = T(n,n) = n*(n-1) + 1, n>=1, and its interior terms via T(r,c) = T(r-1,c) + T(r-1,c-1)+ T(r-2,c-1), 2<=cJ. M. Bergot, Mar 16 2013

Crossrefs

Row 2 of A292357.
Column sums of A059678.
Cf. A001333, A034184, A034187, A052542 (first differences).

Programs

  • Haskell
    a034182 n = a034182_list !! (n-1)
    a034182_list = 1 : 5 : (map (+ 4) $
       zipWith (+) a034182_list (map (* 2) $ tail a034182_list))
    -- Reinhard Zumkeller, May 23 2013
  • Mathematica
    {1}~Join~NestList[{#2, 2 #2 + #1 + 4} & @@ # &, {1, 5}, 28][[All, -1]] (* Michael De Vlieger, Oct 02 2017 *)

Formula

a(n) = 2a(n-1) + a(n-2) + 4.
(1 + 5x + 15x^2 + ...) = (1 + 2x + 2x^2 + ...) * (1 + 3x + 7x^2 + ...), convolution of A040000 and left-shifted A001333.
a(n) = (-4 + (1-sqrt(2))^(1+n) + (1+sqrt(2))^(1+n))/2. G.f.: x*(1+x)^2/((1-x)*(1 - 2*x - x^2)). - Colin Barker, May 22 2012
a(n) = A001333(n+1)-2. - R. J. Mathar, Mar 28 2013
a(n) = A048739(n-3) +2*A048739(n-2) +A048739(n-1). - R. J. Mathar, Jun 15 2020

A069325 Number of 3 X n binary arrays with path of adjacent 1's from upper right corner to lower left corner.

Original entry on oeis.org

1, 8, 51, 295, 1632, 8830, 47239, 251261, 1332456, 7055228, 37327007, 197404203, 1043751584, 5518106750, 29171471659, 154210451661, 815197197636, 4309313949364, 22779900825195, 120418887728947
Offset: 1

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Author

R. H. Hardin, Mar 16 2002

Keywords

Crossrefs

Row 3 of A359575.
Cf. 2 X n A048739, 4 X n A069326, 5 X n A069327, 6 X n A069328, 7 X n A069329, 8 X n A069330, 9 X n A069331, 10 X n A069332, 11 X n A069333, 12 X n A069334, 13 X n A069335, 14 X n A069336, 15 X n A069337, 16 X n A069338, 17 X n A069339, 18 X n A069340, 19 X n A069341, 20 X n A069342, n X n A069343, n X n symmetric A069344.

Programs

  • Magma
    m:=25; R:=PowerSeriesRing(Integers(), m); Coefficients(R!(x*(1-x+x^3)/((1-2*x-2*x^2)*(2*x^5-4*x^4+x^3+9*x^2-7*x+1)))); // G. C. Greubel, Apr 22 2018
  • Mathematica
    CoefficientList[Series[x*(1-x+x^3)/((1-2*x-2*x^2)*(2*x^5-4*x^4+x^3+9*x^2 -7*x+1)), {x, 0, 50}], x] (* G. C. Greubel, Apr 22 2018 *)
    LinearRecurrence[{9,-21,3,24,-8,-4,4},{1,8,51,295,1632,8830,47239},20] (* Harvey P. Dale, May 21 2023 *)
  • PARI
    Vec(-x*(1-x+x^3)/(2*x^2+2*x-1)/(2*x^5-4*x^4+x^3+9*x^2-7*x+1) + O(x^99)) \\ Charles R Greathouse IV, Jun 12 2015
    

Formula

G.f.: x*(1-x+x^3)/((1-2*x-2*x^2)*(2*x^5-4*x^4+x^3+9*x^2-7*x+1)). - Vladeta Jovovic, Jul 02 2003

A069342 Number of 20 X n binary arrays with path of adjacent 1's from upper right corner to lower left corner.

Original entry on oeis.org

1, 27304196, 120418887728947, 273114307102338469932, 451242636516479543205804329, 625576823311351623848371148927043, 778880000189830517730349450554806038383, 903099763914081099274411192869395521423076059, 995759593882933848778575773902474323196918603122861
Offset: 1

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Author

R. H. Hardin, Mar 16 2002

Keywords

Crossrefs

Cf. 2 X n A048739, 3 X n A069325, 4 X n A069326, 5 X n A069327, 6 X n A069328, 7 X n A069329, 8 X n A069330, 9 X n A069331, 10 X n A069332, 11 X n A069333, 12 X n A069334, 13 X n A069335, 14 X n A069336, 15 X n A069337, 16 X n A069338, 17 X n A069339, 18 X n A069340, 19 X n A069341, n X n A069343, n X n symmetric A069344.

Extensions

a(5)-a(9) from Sean A. Irvine, Apr 28 2024

A214992 Power ceiling-floor sequence of (golden ratio)^4.

Original entry on oeis.org

7, 47, 323, 2213, 15169, 103969, 712615, 4884335, 33477731, 229459781, 1572740737, 10779725377, 73885336903, 506417632943, 3471038093699, 23790849022949, 163064905066945, 1117663486445665, 7660579500052711
Offset: 0

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Author

Clark Kimberling, Nov 08 2012, Jan 24 2013

Keywords

Comments

Let f = floor and c = ceiling. For x > 1, define four sequences as functions of x, as follows:
p1(0) = f(x), p1(n) = f(x*p1(n-1));
p2(0) = f(x), p2(n) = c(x*p2(n-1)) if n is odd and p2(n) = f(x*p1(n-1)) if n is even;
p3(0) = c(x), p3(n) = f(x*p3(n-1)) if n is odd and p3(n) = c(x*p3(n-1)) if n is even;
p4(0) = c(x), p4(n) = c(x*p4(n-1)).
The present sequence is given by a(n) = p3(n).
Following the terminology at A214986, call the four sequences power floor, power floor-ceiling, power ceiling-floor, and power ceiling sequences. In the table below, a sequence is identified with an A-numbered sequence if they appear to agree except possibly for initial terms. Notation: S(t)=sqrt(t), r = (1+S(5))/2 = golden ratio, and Limit = limit of p3(n)/p2(n).
x ......p1..... p2..... p3..... p4.......Limit
r^2.....A001519 A001654 A061646 A001906..-1+S(5)
r^3.....A024551 A001076 A015448 A049652..-1+S(5)
r^4.....A049685 A157335 A214992 A004187..-19+9*S(5)
r^5.....A214993 A049666 A015457 A214994...(-9+5*S(5))/2
r^6.....A007805 A156085 A214995 A049660..-151+68*S(5)
2+S(2)..A007052 A214996 A214997 A007070..(1+S(2))/2
1+S(3)..A057960 A002605 A028859 A077846..(1+S(3))/2
2+S(3)..A001835 A109437 A214998 A001353..-4+3*S(3)
S(5)....A214999 A215091 A218982 A218983..1.26879683...
2+S(5)..A024551 A001076 A015448 A049652..-1+S(5)
2+S(6)..A218984 A090017 A123347 A218985..S(3/2)
2+S(7)..A218986 A015530 A126473 A218987..(1+S(7))/3
2+S(8)..A218988 A057087 A086347 A218989..(1+S(2))/2
3+S(8)..A001653 A084158 A218990 A001109..-13+10*S(2)
3+S(10).A218991 A005668 A015451 A218992..-2+S(10)
...
Properties of p1, p2, p3, p4:
(1) If x > 2, the terms of p2 and p3 interlace: p2(0) < p3(0) < p2(1) < p3(1) < p2(2) < p3(2)... Also, p1(n) <= p2(n) <= p3(n) <= p4(n) <= p1(n+1) for all x>0 and n>=0.
(2) If x > 2, the limits L(x) = limit(p/x^n) exist for the four functions p(x), and L1(x) <= L2(x) <= L3(x) <= L4 (x). See the Mathematica programs for plots of the four functions; one of them also occurs in the Odlyzko and Wilf article, along with a discussion of the special case x = 3/2.
(3) Suppose that x = u + sqrt(v) where v is a nonsquare positive integer. If u = f(x) or u = c(x), then p1, p2, p3, p4 are linear recurrence sequences. Is this true for sequences p1, p2, p3, p4 obtained from x = (u + sqrt(v))^q for every positive integer q?
(4) Suppose that x is a Pisot-Vijayaraghavan number. Must p1, p2, p3, p4 then be linearly recurrent? If x is also a quadratic irrational b + c*sqrt(d), must the four limits L(x) be in the field Q(sqrt(d))?
(5) The Odlyzko and Wilf article (page 239) raises three interesting questions about the power ceiling function; it appears that they remain open.

Examples

			a(0) = ceiling(r) = 7, where r = ((1+sqrt(5))/2)^4 = 6.8...; a(1) = floor(7*r) = 47; a(2) = ceiling(47) = 323.
		

Crossrefs

Programs

  • Mathematica
    (* Program 1.  A214992 and related sequences *)
    x = GoldenRatio^4; z = 30; (* z = # terms in sequences *)
    z1 = 100; (* z1 = # digits in approximations *)
    f[x_] := Floor[x]; c[x_] := Ceiling[x];
    p1[0] = f[x]; p2[0] = f[x]; p3[0] = c[x]; p4[0] = c[x];
    p1[n_] := f[x*p1[n - 1]]
    p2[n_] := If[Mod[n, 2] == 1, c[x*p2[n - 1]], f[x*p2[n - 1]]]
    p3[n_] := If[Mod[n, 2] == 1, f[x*p3[n - 1]], c[x*p3[n - 1]]]
    p4[n_] := c[x*p4[n - 1]]
    Table[p1[n], {n, 0, z}]  (* A049685 *)
    Table[p2[n], {n, 0, z}]  (* A157335 *)
    Table[p3[n], {n, 0, z}]  (* A214992 *)
    Table[p4[n], {n, 0, z}]  (* A004187 *)
    Table[p4[n] - p1[n], {n, 0, z}]  (* A004187 *)
    Table[p3[n] - p2[n], {n, 0, z}]  (* A098305 *)
    (* Program 2.  Plot of power floor and power ceiling functions, p1(x) and p4(x) *)
    f[x_] := f[x] = Floor[x]; c[x_] := c[x] = Ceiling[x];
    p1[x_, 0] := f[x]; p1[x_, n_] := f[x*p1[x, n - 1]];
    p4[x_, 0] := c[x]; p4[x_, n_] := c[x*p4[x, n - 1]];
    Plot[Evaluate[{p1[x, 10]/x^10, p4[x, 10]/x^10}], {x, 2, 3}, PlotRange -> {0, 4}]
    (* Program 3. Plot of power floor-ceiling and power ceiling-floor functions, p2(x) and p3(x) *)
    f[x_] := f[x] = Floor[x]; c[x_] := c[x] = Ceiling[x];
    p2[x_, 0] := f[x]; p3[x_, 0] := c[x];
    p2[x_, n_] := If[Mod[n, 2] == 1, c[x*p2[x, n - 1]], f[x*p2[x, n - 1]]]
    p3[x_, n_] := If[Mod[n, 2] == 1, f[x*p3[x, n - 1]], c[x*p3[x, n - 1]]]
    Plot[Evaluate[{p2[x, 10]/x^10, p3[x, 10]/x^10}], {x, 2, 3}, PlotRange -> {0, 4}]

Formula

a(n) = floor(r*a(n-1)) if n is odd and a(n) = ceiling(r*a(n-1)) if n is even, where a(0) = ceiling(r), r = (golden ratio)^4 = (7 + sqrt(5))/2.
a(n) = 6*a(n-1) + 6*a(n-2) - a(n-3).
G.f.: (7 + 5*x - x^2)/((1 + x)*(1 - 7*x + x^2)).
a(n) = (10*(-2)^n+(10+3*sqrt(5))*(7-3*sqrt(5))^(n+2)+(10-3*sqrt(5))*(7+3*sqrt(5))^(n+2))/(90*2^n). - Bruno Berselli, Nov 14 2012
a(n) = 7*A157335(n) + 5*A157335(n-1) - A157335(n-2). - R. J. Mathar, Feb 05 2020
E.g.f.: exp(-x)*(5 + 2*exp(9*x/2)*(155*cosh(3*sqrt(5)*x/2) + 69*sqrt(5)*sinh(3*sqrt(5)*x/2)))/45. - Stefano Spezia, Oct 28 2024

A069326 Number of 4 X n binary arrays with path of adjacent 1's from upper right corner to lower left corner.

Original entry on oeis.org

1, 20, 295, 3828, 46557, 546286, 6279393, 71316632, 804230945, 9031118936, 101161197895, 1131456031256, 12643706576681, 141214773950750, 1576695869980497, 17600838146781308, 196457931325141165
Offset: 1

Views

Author

R. H. Hardin, Mar 16 2002

Keywords

Crossrefs

Row 4 of A359575.
Cf. 2 X n A048739, 3 X n A069325, 5 X n A069327, 6 X n A069328, 7 X n A069329, 8 X n A069330, 9 X n A069331, 10 X n A069332, 11 X n A069333, 12 X n A069334, 13 X n A069335, 14 X n A069336, 15 X n A069337, 16 X n A069338, 17 X n A069339, 18 X n A069340, 19 X n A069341, 20 X n A069342, n X n A069343, n X n symmetric A069344.

A069327 Number of 5 X n binary arrays with path of adjacent 1's from upper right corner to lower left corner.

Original entry on oeis.org

1, 49, 1632, 46557, 1225194, 30754544, 749866185, 17950397258, 424660442975, 9969967594443, 232909647253690, 5423397612311731, 126017939209370356, 2924071505958808678, 67786971099219351975, 1570519781573431498844
Offset: 1

Views

Author

R. H. Hardin, Mar 16 2002

Keywords

Crossrefs

Row 5 of A359575.
Cf. 2 X n A048739, 3 X n A069325, 4 X n A069326, 6 X n A069328, 7 X n A069329, 8 X n A069330, 9 X n A069331, 10 X n A069332, 11 X n A069333, 12 X n A069334, 13 X n A069335, 14 X n A069336, 15 X n A069337, 16 X n A069338, 17 X n A069339, 18 X n A069340, 19 X n A069341, 20 X n A069342, n X n A069343, n X n symmetric A069344.

A069328 Number of 6 X n binary arrays with path of adjacent 1's from upper right corner to lower left corner.

Original entry on oeis.org

1, 119, 8830, 546286, 30754544, 1636193228, 83949041929, 4204804906873, 207204257344200, 10097172081372386, 488256657363269300, 23483738804219826986, 1125283073890577118094
Offset: 1

Views

Author

R. H. Hardin, Mar 16 2002

Keywords

Crossrefs

Cf. 2 X n A048739, 3 X n A069325, 4 X n A069326, 5 X n A069327, 7 X n A069329, 8 X n A069330, 9 X n A069331, 10 X n A069332, 11 X n A069333, 12 X n A069334, 13 X n A069335, 14 X n A069336, 15 X n A069337, 16 X n A069338, 17 X n A069339, 18 X n A069340, 19 X n A069341, 20 X n A069342, n X n A069343, n X n symmetric A069344.

Extensions

a(10)-a(13) from Sean A. Irvine, Apr 27 2024

A069329 Number of 7 X n binary arrays with path of adjacent 1's from upper right corner to lower left corner.

Original entry on oeis.org

1, 288, 47239, 6279393, 749866185, 83949041929, 9009490924794, 939356338522456, 95972872569551099, 9664595615275994739, 963147644297772022870, 95261720343073832781620, 9370213923827917022436855
Offset: 1

Views

Author

R. H. Hardin, Mar 16 2002

Keywords

Crossrefs

Cf. 2 X n A048739, 3 X n A069325, 4 X n A069326, 5 X n A069327, 6 X n A069328, 8 X n A069330, 9 X n A069331, 10 X n A069332, 11 X n A069333, 12 X n A069334, 13 X n A069335, 14 X n A069336, 15 X n A069337, 16 X n A069338, 17 X n A069339, 18 X n A069340, 19 X n A069341, 20 X n A069342, n X n A069343, n X n symmetric A069344.

Extensions

a(8)-a(13) from Sean A. Irvine, Apr 27 2024

A069330 Number of 8 X n binary arrays with path of adjacent 1's from upper right corner to lower left corner.

Original entry on oeis.org

1, 696, 251261, 71316632, 17950397258, 4204804906873, 939356338522456, 203037531986079710, 42856467943438387389, 8890050748561149390768, 1820486395967688826354303, 369211160728496631061072520, 74336348859792978822695533158
Offset: 1

Views

Author

R. H. Hardin, Mar 16 2002

Keywords

Crossrefs

Cf. 2 X n A048739, 3 X n A069325, 4 X n A069326, 5 X n A069327, 6 X n A069328, 7 X n A069329, 9 X n A069331, 10 X n A069332, 11 X n A069333, 12 X n A069334, 13 X n A069335, 14 X n A069336, 15 X n A069337, 16 X n A069338, 17 X n A069339, 18 X n A069340, 19 X n A069341, 20 X n A069342, n X n A069343, n X n symmetric A069344.

Extensions

a(7)-a(13) from Sean A. Irvine, Apr 27 2024
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