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.

Showing 1-10 of 15 results. Next

A089936 Number of 5 X n matrices with entries {0,1} without adjacent 0's in any row or column. 5th row of A089934.

Original entry on oeis.org

13, 99, 827, 6743, 55447, 454385, 3729091, 30584687, 250916131, 2058249165, 16884649135, 138508056265, 1136221529549, 9320704799431, 76460212316453, 627222736888811, 5145271430670385, 42207992410219447, 346243111960194009
Offset: 1

Views

Author

Marc LeBrun, Nov 15 2003

Keywords

Comments

Row/columns 1 through 7 are A000045, A001333, A051736, A051737, A089936, A089937, A089938.
Number of independent vertex sets in the grid graph P_5 X P_n. - Andrew Howroyd, Jun 06 2017

Crossrefs

Formula

G.f.: x*(13 + 47*x - 37*x^2 - 129*x^3 + 68*x^4 + 49*x^5 - 23*x^6 - 3*x^7 + x^8) / (1 - 4*x - 36*x^2 + 105*x^4 - 15*x^5 - 64*x^6 + 20*x^7 + 4*x^8 - x^9) (conjectured). - Colin Barker, Jun 06 2017
The above conjecture is correct since the order of the recurrence is A089935(5) = 9. - Andrew Howroyd, Dec 24 2019

A089937 Number of 6 X n matrices with entries {0,1} without adjacent 0's in any row or column. 6th row of A089934.

Original entry on oeis.org

21, 239, 2999, 36787, 454385, 5598861, 69050253, 851302029, 10496827403, 129422885699, 1595777230271, 19675706193157, 242599324206721, 2991220223776445, 36881397137844409, 454743263319217787, 5606930966068061311, 69132797971282998447
Offset: 1

Views

Author

Marc LeBrun, Nov 15 2003

Keywords

Comments

Row/columns 1 through 7 are A000045, A001333, A051736, A051737, A089936, A089937, A089938.
Number of independent vertex sets in the grid graph P_6 X P_n. - Andrew Howroyd, Jun 06 2017

Crossrefs

Formula

G.f.: x*(21 + 71*x - 215*x^2 - 385*x^3 + 668*x^4 + 234*x^5 - 400*x^6 + 9*x^7 + 49*x^8 - 3*x^9 - x^10) / (1 - 8*x - 62*x^2 + 78*x^3 + 375*x^4 - 300*x^5 - 486*x^6 + 385*x^7 + 30*x^8 - 52*x^9 + 2*x^10 + x^11) (conjectured). - Colin Barker, Jun 06 2017
The above conjecture is correct because the order of the recurrence is A089935(6) = 11. - Andrew Howroyd, Dec 24 2019

Extensions

Terms a(17) and beyond from Andrew Howroyd, Jun 06 2017

A089938 Number of 7 X n matrices with entries {0,1} without adjacent 0's in any row or column. 7th row of A089934.

Original entry on oeis.org

34, 577, 10897, 200798, 3729091, 69050253, 1280128950, 23720149995, 439621976195, 8147000813446, 150985649174085, 2798109826697003, 51855860689753372, 961012671564107667, 17809889025037476097, 330060028036299469334, 6116807668464485142495
Offset: 1

Views

Author

Marc LeBrun, Nov 15 2003

Keywords

Comments

Row/columns 1 through 7 are A000045, A001333, A051736, A051737, A089936, A089937, A089938.
Number of independent vertex sets in the grid graph P_7 X P_n. - Andrew Howroyd, Jun 06 2017

Crossrefs

Formula

O.g.f.: - (X - 1)*(X^19 + 10*X^18 - 58*X^17 - 576*X^16 + 651*X^15 + 8054*X^14 - 5381*X^13 - 42910*X^12 + 32530*X^11 + 90357*X^10 - 90813*X^9 - 52366*X^8 + 79558*X^7 - 8263*X^6 - 13918*X^5 + 2501*X^4 + 894*X^3 - 94*X^2 - 26*X - 1)/(X^21 + 9*X^20 - 87*X^19 - 546*X^18 + 2227*X^17 + 9369*X^16 - 25564*X^15 - 54187*X^14 + 139011*X^13 + 100779*X^12 - 340142*X^11 + 21372*X^10 + 308107*X^9 - 127405*X^8 - 82823*X^7 + 48558*X^6 + 6975*X^5 - 5659*X^4 - 210*X^3 + 203*X^2 + 9*X - 1)

Extensions

Terms a(16) and beyond from Andrew Howroyd, Jun 06 2017

A089935 a(n) = order of recurrence generating row (or column) n of A089934.

Original entry on oeis.org

2, 2, 4, 5, 9, 11, 21, 30, 51, 76, 127, 195, 322, 504, 826
Offset: 1

Views

Author

Marc LeBrun, Nov 15 2003

Keywords

Comments

The only known value where a(n) is strictly less than the theoretical upper bound A001224(n+1) is a(6) = 11. - Andrew Howroyd, Dec 24 2019

Examples

			a(2)=2 because the recurrence relation for the second row/column is a(n) = 2 a(n-1) + a(n-2).
		

Crossrefs

Row/columns 1 through 7 of A089934 are A000045, A001333, A051736, A051737, A089936, A089937, A089938.
Cf. A001224.

Formula

a(n) <= A001224(n+1). - Andrew Howroyd, Dec 24 2019

Extensions

a(8)-a(10) from Andrew Howroyd, Dec 24 2019
a(11)-a(15) from Max Alekseyev, Dec 12 2024

A006506 Number of n X n binary matrices with no 2 adjacent 1's, or number of configurations of non-attacking princes on an n X n board, where a "prince" attacks the four adjacent (non-diagonal) squares. Also number of independent vertex sets in an n X n grid.

Original entry on oeis.org

1, 2, 7, 63, 1234, 55447, 5598861, 1280128950, 660647962955, 770548397261707, 2030049051145980050, 12083401651433651945979, 162481813349792588536582997, 4935961285224791538367780371090, 338752110195939290445247645371206783, 52521741712869136440040654451875316861275
Offset: 0

Views

Author

Keywords

Comments

A two-dimensional generalization of the Fibonacci numbers.
Also the number of vertex covers in the n X n grid graph P_n X P_n.
A181030 (Number of n X n binary matrices with no leading bitstring in any row or column divisible by 4) is the same sequence. Proof from Steve Butler, Jan 26 2015: This is trivially true. A181030 is equivalent to this sequence by interchanging the roles of 0 and 1. In particular, A181030 looks for binary matrices with no leading bitstring divisible by 4, but a bitstring is divisible by 4 if and only if its last two digits is 0; in a binary matrix this can only be avoided if there are no two adjacent 0's (i.e., for any two adjacent 0's take the bitstring starting in that row or column and we are done); the present sequence looks for no two adjacent 1's. Similar reasons show that the array A181031 is equivalent to the array A089980.
Let R(n) be the set of squares that have vertices at integer coordinates and lie in the region of the plane |x|+|y| <= n+1, and let S(n) be the set of squares that have vertices at integer coordinates and lie in the region of the plane |x|+|y-1/2| <= n+2. Further let T be the collection of rectangular tiles with dimensions i X 1 or 1 X i with i arbitrary. Then a(2n) is the number of ways to tile R(n) using tiles from T and a(2n+1) is the number of ways to tile S(n) using tiles from T. (Note R(n) is the Aztec diamond of order n.) - Steve Butler, Jan 26 2015

References

  • Steven R. Finch, Mathematical Constants, Cambridge, 2003, pp. 342-349.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A027683 for toroidal version.
Table of values for n x m matrices: A089934.
Cf. A232833 for refinement by number of 1's.
Cf. also A191779.

Programs

  • Maple
    A006506 := proc(N) local i,j,p,q; p := 1+x11;
    if n=0 then return 1 fi;
    for i from 2 to N do
       q := p-select(has,p,x||(i-1)||1);
       p := p+expand(q*x||i||1)
    od;
    for j from 2 to N do
       q := p-select(has,p,x1||(j-1));
       p := subs(x1||(j-1)=1,p)+expand(q*x1||j);
       for i from 2 to N do
          q := p-select(has,p,{x||(i-1)||j,x||i||(j-1)});
          p := subs(x||i||(j-1)=1,p)+expand(q*x||i||j);
       od
    od;
    map(icontent,p)
    end:
    seq(A006506(n), n=0..15);
  • Mathematica
    a[n_] := a[n] = (p = 1 + x[1, 1]; Do[q = p - Select[p, ! FreeQ[#, x[i-1, 1]] &]; p = p + Expand[q*x[i, 1]], {i, 2, n}]; Do[q = p - Select[p, ! FreeQ[#, x[1, j-1]] &]; p = (p /. x[i, j-1] :> 1) + Expand[q*x[1, j]]; Do[q = p - Select[ p, ! FreeQ[#, x[i-1, j]] || ! FreeQ[#, x[i, j-1]] &]; p = (p /. x[i, j-1] :> 1) + Expand[q*x[i, j]], {i, 2, n}], {j, 2, n}]; p /. x[, ] -> 1); a /@ Range[14] (* Jean-François Alcover, May 25 2011, after Maple prog. *)
    Table[With[{g = GridGraph[{n, n}]}, Count[Subsets[Range[n^2], Length @ First @ FindIndependentVertexSet[g]], ?(IndependentVertexSetQ[g, #] &)]], {n, 5}] (* _Eric W. Weisstein, May 28 2017 *)
  • PARI
    a(n)=L=fibonacci(n+2);p=v=vector(L,i,1);c=0; for(i=0,2^n-1,j=i;while(j&&j%4<3,j\=2);if(j%4<3,p[c++]=i)); for(i=2,n,w=vector(L,j,0); for(j=1,L, for(k=1,L,if(bitand(p[j],p[k])==0,w[j]+=v[k])));v=w); sum(i=1,L,v[i]) \\ Robert Gerbicz, Jun 17 2011

Formula

Limit_{n->oo} a(n)^(1/n^2) = c1 = 1.50304... is the hard square entropy constant A085850. - Benoit Cloitre, Nov 16 2003
a(n) appears to behave like A * c3^n * c1^(n^2) where c1 is as above, c3 = 1.143519129587 approximately, A = 1.0660826 approximately. This is based on numerical analysis of a(n) for n up to 19. - Brendan McKay, Nov 16 2003
From n up to 39 we have A = 1.06608266035... - Vaclav Kotesovec, Jan 29 2024

Extensions

Sequence extended by Paul Zimmermann, Mar 15 1996
Maple program updated and sequence extended by Robert Israel, Jun 16 2011
a(0)=1 prepended by Alois P. Heinz, Jan 29 2024

A218354 T(n,k) = Hilltop maps: number of nXk binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or vertical neighbor in a random 0..1 n X k array.

Original entry on oeis.org

1, 3, 3, 5, 11, 5, 9, 41, 41, 9, 17, 149, 291, 149, 17, 31, 547, 2069, 2069, 547, 31, 57, 2007, 14811, 28661, 14811, 2007, 57, 105, 7361, 105913, 401253, 401253, 105913, 7361, 105, 193, 27001, 757305, 5609569, 10982565, 5609569, 757305, 27001, 193, 355
Offset: 1

Views

Author

R. H. Hardin, Oct 26 2012

Keywords

Comments

From Andrew Howroyd, May 10 2017: (Start)
Number of n X k binary matrices with every 1 vertically or horizontally adjacent to some 0.
Number of dominating sets in the grid graph P_n X P_k. (End)

Examples

			Table starts
....1.......3...........5..............9.................17
....3......11..........41............149................547
....5......41.........291...........2069..............14811
....9.....149........2069..........28661.............401253
...17.....547.......14811.........401253...........10982565
...31....2007......105913........5609569..........300126903
...57....7361......757305.......78394141.........8199377227
..105...27001.....5415209.....1095695529.......224032447213
..193...99043....38722037....15314367301......6121258910011
..355..363299...276885777...214044940145....167250519310183
..653.1332617..1979899795..2991651891557...4569773233045519
.1201.4888173.14157473937.41813576818545.124859601874166153
...
Some solutions for n=3 k=4
..1..0..1..1....1..1..1..0....1..1..1..0....1..0..1..1....1..0..1..1
..1..0..1..0....1..0..1..0....0..0..1..0....1..0..1..1....1..1..0..1
..0..0..1..0....1..1..0..1....0..1..1..1....1..1..1..1....1..1..1..0
		

Crossrefs

Columns 1-7 are A000213(n+1), A218348, A218349, A218350, A218351, A218352, A218353.
Diagonal is A133515.
Cf. A089934 (independent vertex sets), A210662 (matchings).

Formula

Empirical for column k:
k=1: a(n) = a(n-1) +a(n-2) +a(n-3).
k=2: a(n) = 3*a(n-1) +2*a(n-2) +2*a(n-3) -a(n-4) -a(n-5).
k=3: a(n) = 6*a(n-1) +5*a(n-2) +22*a(n-3) +7*a(n-4) +8*a(n-5) -18*a(n-6) -20*a(n-7) -a(n-8) +4*a(n-9) +3*a(n-10) +a(n-12).
Column k=1 for an underlying 0..z array: a(n) = sum(i=1..2z+1){a(n-i)} z=1,2,3,4

A197054 T(n,k)=Number of nXk 0..4 arrays with each element equal to the number of its horizontal and vertical zero neighbors.

Original entry on oeis.org

1, 2, 2, 2, 2, 2, 3, 4, 4, 3, 4, 6, 10, 6, 4, 5, 10, 18, 18, 10, 5, 7, 16, 38, 42, 38, 16, 7, 9, 26, 78, 108, 108, 78, 26, 9, 12, 42, 156, 274, 358, 274, 156, 42, 12, 16, 68, 320, 692, 1132, 1132, 692, 320, 68, 16, 21, 110, 654, 1754, 3580, 4468, 3580, 1754, 654, 110, 21, 28
Offset: 1

Views

Author

R. H. Hardin, Oct 09 2011

Keywords

Comments

Every 0 is next to 0 0's, every 1 is next to 1 0's, every 2 is next to 2 0's, every 3 is next to 3 0's, every 4 is next to 4 0's
Also, the number of maximal independent vertex sets in the grid graph P_n X P_k. - Andrew Howroyd, May 16 2017

Examples

			Table starts
..1...2....2.....3......4.......5........7.........9.........12..........16
..2...2....4.....6.....10......16.......26........42.........68.........110
..2...4...10....18.....38......78......156.......320........654........1326
..3...6...18....42....108.....274......692......1754.......4442.......11248
..4..10...38...108....358....1132.....3580.....11382......36270......114992
..5..16...78...274...1132....4468....17742.....70616.....281202.....1117442
..7..26..156...692...3580...17742....88056....439338....2192602....10912392
..9..42..320..1754..11382...70616...439338...2745186...17155374...106972582
.12..68..654..4442..36270..281202..2192602..17155374..134355866..1049189170
.16.110.1326.11248.114992.1117442.10912392.106972582.1049189170.10264692132
...
Some solutions for n=6 k=4
..0..2..1..0....0..2..0..1....2..0..2..0....0..3..0..2....0..2..1..0
..2..0..1..2....1..1..1..1....0..2..1..1....2..0..4..0....3..0..1..2
..1..1..2..0....1..0..2..0....2..1..0..2....1..2..0..2....0..3..1..0
..0..3..0..3....1..1..1..1....0..2..2..0....0..1..1..1....2..0..1..2
..3..0..4..0....0..3..0..2....3..0..1..2....1..1..1..0....1..1..2..0
..0..3..0..2....2..0..3..0....0..2..1..0....1..0..1..1....0..2..0..2
		

Crossrefs

Column 1 is A000931(n+6).
Column 2 is A006355(n+1).
Columns 3-7 are A197049, A197050, A197051, A197052, A197053.
Main diagonal is A197048.
Cf. A089934 (independent sets), A218354 (dominating sets).

A286513 Array read by antidiagonals: T(m,n) is the number of independent sets in the stacked prism graph C_m X P_n.

Original entry on oeis.org

1, 1, 3, 1, 7, 4, 1, 17, 13, 7, 1, 41, 43, 35, 11, 1, 99, 142, 181, 81, 18, 1, 239, 469, 933, 621, 199, 29, 1, 577, 1549, 4811, 4741, 2309, 477, 47, 1, 1393, 5116, 24807, 36211, 26660, 8303, 1155, 76, 1, 3363, 16897, 127913, 276561, 307983, 143697, 30277, 2785, 123
Offset: 1

Views

Author

Andrew Howroyd, May 10 2017

Keywords

Comments

Equivalently, the number of vertex covers in the stacked prism graph C_m X P_n.

Examples

			Table starts:
=============================================================
m\n|   1    2     3      4        5         6           7
---|---------------------------------------------------------
1  |   1    1     1      1        1         1           1 ...
2  |   3    7    17     41       99       239         577 ...
3  |   4   13    43    142      469      1549        5116 ...
4  |   7   35   181    933     4811     24807      127913 ...
5  |  11   81   621   4741    36211    276561     2112241 ...
6  |  18  199  2309  26660   307983   3557711    41097664 ...
7  |  29  477  8303 143697  2488431  43089985   746156517 ...
8  |  47 1155 30277 788453 20546803 535404487 13951571713 ...
...
		

Crossrefs

Rows 3..8 are A003688(n+1), A051926, A181989, A181961, A182014, A182019.
Columns 1..4 are A000032, A051927, A050400, A050401.
Main diagonal is A212270.
Cf. A089934 (P_m X P_n), A027683, A286514.

A051736 Number of 3 X n (0,1)-matrices with no consecutive 1's in any row or column.

Original entry on oeis.org

1, 5, 17, 63, 227, 827, 2999, 10897, 39561, 143677, 521721, 1894607, 6879979, 24983923, 90725999, 329460929, 1196397873, 4344577397, 15776816033, 57291635519, 208047769363, 755500774443, 2743511349031, 9962735709201, 36178491743225, 131377896967213, 477083233044745
Offset: 0

Views

Author

Stephen G Penrice, Dec 06 1999

Keywords

Comments

Also the number of independent vertex sets and vertex covers in the 3 X n grid graph. - Eric W. Weisstein, Sep 21 2017

Examples

			There are five 3 X 1 (0,1)-matrices with no consecutive 1's:
  0 0 0
  0 0 1
  0 1 0
  1 0 0
  1 0 1
There are 17 3 X 2 (0,1)-matrices with no consecutive 1's:
0 0, 0 1, 0 0, 0 0, 0 1, 1 0, 1 0, 1 0, 0 0, 0 1, 0 0, 0 1, 0 0, 0 1, 0 0, 1 0, 1 0
0 0, 0 0, 0 1, 0 0, 0 0, 0 0, 0 1, 0 0, 1 0, 1 0, 1 0, 1 0, 0 0, 0 0, 0 1, 0 0, 0 1
0 0, 0 0, 0 0, 0 1, 0 1, 0 0, 0 0, 0 1, 0 0, 0 0, 0 1, 0 1, 1 0, 1 0, 1 0, 1 0, 1 0
		

Crossrefs

Row 3 of A089934. Row sums of A371967.
Cf. A051737.

Programs

  • Haskell
    a051736 n = a051736_list !! (n-1)
    a051736_list = 1 : 5 : 17 : 63 : zipWith (-) (map (* 2) $ drop 2 $
       zipWith (+) (map (* 3) a051736_list) (tail a051736_list)) a051736_list
    -- Reinhard Zumkeller, Apr 02 2012
    
  • Mathematica
    LinearRecurrence[{2, 6, 0, -1}, {1, 5, 17, 63}, 40] (* Harvey P. Dale, Mar 05 2013 *)
    CoefficientList[Series[(1 + 3 x + x^2 - x^3)/(1 - 2 x - 6 x^2 + x^4), {x, 0, 20}], x] (* Eric W. Weisstein, Sep 21 2017 *)
    Table[-RootSum[1 - 6 #1^2 - 2 #1^3 + #1^4 &, 263 #1^n - 657 #1^(n + 1) - 331 #1^(n + 2) + 81 #1^(n + 3) &]/1994, {n, 0, 20}] (* Eric W. Weisstein, Sep 21 2017 *)
  • PARI
    Vec((1+3*x+x^2-x^3)/(1-2*x-6*x^2+x^4)+O(x^50)) \\ Michel Marcus, Sep 17 2014

Formula

a(n) = 2*a(n-1) + 6*a(n-2) - a(n-4).
G.f.: (1+x)*(1+2*x-x^2)/(1-2*x-6*x^2+x^4). - Philippe Deléham, Sep 07 2006

Extensions

More terms from James Sellers, Dec 08 1999
More terms from Michel Marcus, Sep 17 2014
Offset fixed by Eric W. Weisstein, Sep 21 2017

A286847 Array read by antidiagonals: T(m,n) = number of minimal dominating sets in the grid graph P_m X P_n.

Original entry on oeis.org

1, 2, 2, 2, 6, 2, 4, 7, 7, 4, 4, 18, 16, 18, 4, 7, 39, 53, 53, 39, 7, 9, 75, 154, 306, 154, 75, 9, 13, 155, 436, 1167, 1167, 436, 155, 13, 18, 310, 1268, 4939, 6958, 4939, 1268, 310, 18, 25, 638, 3660, 21313, 40931, 40931, 21313, 3660, 638, 25
Offset: 1

Views

Author

Andrew Howroyd, Aug 01 2017

Keywords

Examples

			Table begins:
===============================================================
m\n|  1   2    3     4       5        6         7          8
---|-----------------------------------------------------------
1  |  1   2    2     4       4        7         9         13...
2  |  2   6    7    18      39       75       155        310...
3  |  2   7   16    53     154      436      1268       3660...
4  |  4  18   53   306    1167     4939     21313      88161...
5  |  4  39  154  1167    6958    40931    254754    1519544...
6  |  7  75  436  4939   40931   349178   3118754   26797630...
7  |  9 155 1268 21313  254754  3118754  40307167  497709474...
8  | 13 310 3660 88161 1519544 26797630 497709474 8863408138...
...
		

Crossrefs

Rows 1-3 are A253412, A290379, A286848.
Main diagonal is A290382.
Cf. A218354 (dominating sets), A089934 (independent), A286868 (irredundant).
Cf. A286849 (king graph).
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