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 10 results.

A250662 Number A(n,k) of tilings of a 2k X n rectangle using 2n k-ominoes of shape I; square array A(n,k), n>=0, k>=0, read by antidiagonals.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 1, 1, 11, 1, 1, 1, 1, 1, 6, 36, 1, 1, 1, 1, 1, 1, 13, 95, 1, 1, 1, 1, 1, 1, 7, 22, 281, 1, 1, 1, 1, 1, 1, 1, 15, 64, 781, 1, 1, 1, 1, 1, 1, 1, 8, 25, 155, 2245, 1, 1, 1, 1, 1, 1, 1, 1, 17, 37, 321, 6336, 1, 1
Offset: 0

Views

Author

Alois P. Heinz, Nov 26 2014

Keywords

Examples

			Square array A(n,k) begins:
  1, 1,    1,   1,   1,  1,  1,  1,  1, ...
  1, 1,    1,   1,   1,  1,  1,  1,  1, ...
  1, 1,    5,   1,   1,  1,  1,  1,  1, ...
  1, 1,   11,   6,   1,  1,  1,  1,  1, ...
  1, 1,   36,  13,   7,  1,  1,  1,  1, ...
  1, 1,   95,  22,  15,  8,  1,  1,  1, ...
  1, 1,  281,  64,  25, 17,  9,  1,  1, ...
  1, 1,  781, 155,  37, 28, 19, 10,  1, ...
  1, 1, 2245, 321, 100, 41, 31, 21, 11, ...
		

Crossrefs

Columns k=0+1,2-10 give: A000012, A005178(n+1), A236577, A236582, A247117, A250663, A250664, A250665, A250666, A250667.
Cf. A251072.

Programs

  • Maple
    b:= proc(n, l) option remember; local d, k; d:= nops(l)/2;
          if n=0 then 1
        elif min(l[])>0 then (m->b(n-m, map(x->x-m, l)))(min(l[]))
        else for k while l[k]>0 do od;
             `if`(nd+1 or max(l[k..k+d-1][])>0, 0,
              b(n, [l[1..k-1][],1$d,l[k+d..2*d][]]))
          fi
        end:
    A:= (n, k)-> `if`(k=0, 1, b(n, [0$2*k])):
    seq(seq(A(n,d-n), n=0..d), d=0..14);
  • Mathematica
    b[n_, l_List] := b[n, l] = Module[{d = Length[l]/2, k}, Which[n == 0, 1, Min[l] > 0 , Function[{m}, b[n-m, l-m]][Min[l]], True, For[k=1, l[[k]] > 0, k++]; If[n d]]] + If[d == 1 || k > d+1 || Max[l[[k ;; k+d-1]]] > 0, 0, b[n, Join[l[[1 ;; k-1]], Array[1&, d], l[[k+d ;; 2*d]]]]]]]; A[n_, k_] := If[k == 0, 1, b[n, Array[0&, 2k]]]; Table[Table[A[n, d-n], {n, 0, d}], {d, 0, 14}] // Flatten (* Jean-François Alcover, Jan 30 2015, after Alois P. Heinz *)

A028468 Number of perfect matchings in graph P_{6} X P_{n}.

Original entry on oeis.org

1, 1, 13, 41, 281, 1183, 6728, 31529, 167089, 817991, 4213133, 21001799, 106912793, 536948224, 2720246633, 13704300553, 69289288909, 349519610713, 1765722581057, 8911652846951, 45005025662792, 227191499132401, 1147185247901449, 5791672851807479
Offset: 0

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Author

Keywords

References

  • F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.
  • R. P. Stanley, Enumerative Combinatorics I, p. 292.

Crossrefs

Row 6 of arrays A099390, A189006.
Column k=2 of A251072.
Cf. A005178.

Programs

  • Magma
    m:=30; R:=PowerSeriesRing(Integers(), m); Coefficients(R!( (x^2-2*x-1)*(x^4+2*x^3-3*x^2-2*x+1)/((1-x^2)*(x^3-5*x^2+6*x-1)*(x^3+ 6*x^2+5*x+1)) )); // G. C. Greubel, Nov 25 2018
    
  • Maple
    seq(coeff(series((1+2*x-x^2)*(x^4+2*x^3-3*x^2-2*x+1)/((x-1)*(x+1)*(x^3-5*x^2+6*x-1)*(x^3+6*x^2+5*x+1)),x,n+1), x, n), n = 0 .. 25); # Muniru A Asiru, Nov 23 2018
  • Mathematica
    a[n_] := Product[2(2 + Cos[(2 k Pi)/7] + Cos[(2 j Pi)/(n+1)]), {k, 1, 3}, {j, 1, n/2}] // Round;
    Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Aug 19 2018, after A099390 *)
    LinearRecurrence[{1, 20, 10, -38, -10, 20, -1, -1}, {1, 1, 13, 41, 281, 1183, 6728, 31529}, 30] (* Vincenzo Librandi, Nov 24 2018 *)
  • PARI
    my(x='x+O('x^30)); Vec(-(x^2-2*x-1)*(x^4+2*x^3-3*x^2-2*x+1)/((x-1)*(1+x)*(x^3-5*x^2+6*x-1)*(x^3+6*x^2+5*x+1))) \\ Altug Alkan, Mar 23 2016
    
  • Sage
    s=((x^2-2*x-1)*(x^4+2*x^3-3*x^2-2*x+1)/((1-x^2)*(x^3-5*x^2+6*x-1) *(x^3+6*x^2+5*x+1))).series(x,30); s.coefficients(x, sparse=False) # G. C. Greubel, Nov 25 2018

Formula

From N. J. A. Sloane, Feb 03 2009: (Start)
a(1) = 1,
a(2) = 13,
a(3) = 41,
a(4) = 281,
a(5) = 1183,
a(6) = 6728,
a(7) = 31529,
a(8) = 167089,
a(9) = 817991,
a(10) = 4213133,
a(11) = 21001799,
a(12) = 106912793,
a(13) = 536948224,
a(14) = 2720246633, and
a(n) = 40*a(n-2) - 416*a(n-4) + 1224*a(n-6) - 1224*a(n-8) + 416*a(n-10) - 40*a(n-12) + a(n-14). (From Faase's web page.) (End)
G.f.: (x^2-2*x-1)*(x^4+2*x^3-3*x^2-2*x+1) / ( (1-x) *(1+x) *(x^3-5*x^2+6*x-1) *(x^3+6*x^2+5*x+1) ).
a(n) = a(n-1)+20*a(n-2)+10*a(n-3)-38*a(n-4)-10*a(n-5)+20*a(n-6)-a(n-7)-a(n-8). - Sergey Perepechko, Sep 23 2018

A251074 Number of tilings of a 12 X n rectangle using 3n tetrominoes of shape I.

Original entry on oeis.org

1, 1, 1, 1, 26, 75, 154, 269, 1732, 5764, 15131, 34345, 135950, 462186, 1356284, 3539433, 11681091, 38519022, 118366429, 334591568, 1037603086, 3309045401, 10296063522, 30414763937, 92735958046, 289374852696, 899439481823, 2716896548850, 8270384213984
Offset: 0

Views

Author

Alois P. Heinz, Nov 29 2014

Keywords

Crossrefs

Column k=4 of A251072.
Cf. A236582.

A247218 Number of tilings of a 15 X n rectangle using 3n pentominoes of shape I.

Original entry on oeis.org

1, 1, 1, 1, 1, 34, 95, 190, 325, 506, 3324, 10353, 25607, 55346, 108756, 389216, 1208901, 3281686, 8006108, 17950204, 51430928, 150609259, 419540401, 1090827453, 2651884943, 7077981621, 19691707908, 54499735145, 145671654672, 371632691473, 976543067070
Offset: 0

Views

Author

Alois P. Heinz, Nov 26 2014

Keywords

Crossrefs

Column k=5 of A251072.

A251073 Number of tilings of a 9 X n rectangle using 3n trominoes of shape I.

Original entry on oeis.org

1, 1, 1, 19, 57, 121, 783, 2861, 8133, 37160, 143419, 468816, 1876855, 7263468, 25496863, 97187247, 372086645, 1352780401, 5071962134, 19220628318, 71025008365, 265095817718, 997839772024, 3713274525679, 13851695644227, 51940567251136, 193830054345968
Offset: 0

Views

Author

Alois P. Heinz, Nov 29 2014

Keywords

Crossrefs

Column k=3 of A251072.
Cf. A236577.

Programs

  • Maple
    # see link above.

Formula

G.f.: see link above.

A251075 Number of tilings of a 18 X n rectangle using 3n hexominoes of shape I.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 43, 117, 229, 385, 591, 853, 5789, 17163, 40521, 84211, 160143, 284639, 945352, 2743255, 7017326, 16250983, 34801374, 69959957, 179843441, 479965811, 1238082783, 3015746329, 6925030997, 15065972891, 35869626723, 89673470947, 226122534275
Offset: 0

Views

Author

Alois P. Heinz, Nov 29 2014

Keywords

Crossrefs

Column k=6 of A251072.
Cf. A250663.

A251076 Number of tilings of a 21 X n rectangle using 3n heptominoes of shape I.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 53, 141, 271, 449, 681, 973, 1331, 9391, 26803, 60953, 122641, 226921, 394031, 650413, 2039288, 5611209, 13694084, 30417897, 62763334, 122046063, 225958222, 532867801, 1319078776, 3196149101, 7383041514, 16186545853, 33788903208
Offset: 0

Views

Author

Alois P. Heinz, Nov 29 2014

Keywords

Crossrefs

Column k=7 of A251072.
Cf. A250664.

A251077 Number of tilings of a 24 X n rectangle using 3n octominoes of shape I.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 64, 167, 316, 517, 776, 1099, 1492, 1961, 14428, 39956, 88103, 172509, 311816, 530678, 860861, 1342433, 4020710, 10599604, 24896626, 53438385, 106915866, 202198270, 365048944, 633709553, 1392777233, 3238633334, 7446642085, 16454751188
Offset: 0

Views

Author

Alois P. Heinz, Nov 29 2014

Keywords

Crossrefs

Column k=8 of A251072.
Cf. A250665.

A251078 Number of tilings of a 27 X n rectangle using 3n nonominoes of shape I.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 76, 195, 364, 589, 876, 1231, 1660, 2169, 2764, 21232, 57379, 123291, 235860, 417784, 698657, 1116149, 1717276, 2559760, 7386240, 18797731, 42769684, 89201688, 173879976, 321141337, 567405676, 965768880, 1591873744, 3298800992
Offset: 0

Views

Author

Alois P. Heinz, Nov 29 2014

Keywords

Crossrefs

Column k=9 of A251072.
Cf. A250666.

A251079 Number of tilings of a 30 X n rectangle using 3n decominoes of shape I.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 89, 225, 415, 665, 981, 1369, 1835, 2385, 3025, 3761, 30169, 79903, 167957, 314911, 548011, 902339, 1422073, 2161837, 3188141, 4580911, 12815576, 31665861, 70135406, 142741143, 272097694, 492367347, 853768306, 1428360119
Offset: 0

Views

Author

Alois P. Heinz, Nov 29 2014

Keywords

Crossrefs

Column k=10 of A251072.
Cf. A250667.
Showing 1-10 of 10 results.