A245013 Number A(n,k) of tilings of a k X n rectangle using 1 X 1 squares and 2 X 2 squares; square array A(n,k), n>=0, k>=0, read by antidiagonals.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 3, 3, 1, 1, 1, 1, 5, 5, 5, 1, 1, 1, 1, 8, 11, 11, 8, 1, 1, 1, 1, 13, 21, 35, 21, 13, 1, 1, 1, 1, 21, 43, 93, 93, 43, 21, 1, 1, 1, 1, 34, 85, 269, 314, 269, 85, 34, 1, 1, 1, 1, 55, 171, 747, 1213, 1213, 747, 171, 55, 1, 1

Offset

0,13

Links

Alois P. Heinz, Antidiagonals n = 0..45, flattened

R. J. Mathar, Tiling n x m rectangles with 1 x 1 and s x s squares, arXiv:1609.03964 [math.CO], 2016.

J. Nilsson, On Counting the Number of Tilings of a Rectangle with Squares of Size 1 and 2, Journal of Integer Sequences, Vol. 20 (2017), Article 17.2.2.

Example

A(3,3) = 5:
  ._._._.  .___._.  ._.___.  ._._._.  ._._._.
  |_|_|_|  |   |_|  |_|   |  |_|_|_|  |_|_|_|
  |_|_|_|  |___|_|  |_|___|  |_|   |  |   |_|
  |_|_|_|  |_|_|_|  |_|_|_|  |_|___|  |___|_| .
Square array A(n,k) begins:
  1, 1,  1,  1,   1,    1,     1,      1, ...
  1, 1,  1,  1,   1,    1,     1,      1, ...
  1, 1,  2,  3,   5,    8,    13,     21, ...
  1, 1,  3,  5,  11,   21,    43,     85, ...
  1, 1,  5, 11,  35,   93,   269,    747, ...
  1, 1,  8, 21,  93,  314,  1213,   4375, ...
  1, 1, 13, 43, 269, 1213,  6427,  31387, ...
  1, 1, 21, 85, 747, 4375, 31387, 202841, ...

Maple

b:= proc(n, l) option remember; local m, k; m:= min(l[]);
      if m>0 then b(n-m, map(x->x-m, l))
    elif n=0 then 1
    else for k while l[k]>0 do od; b(n, subsop(k=1, l))+
         `if`(n>1 and k<nops(l) and l[k+1]=0,
         b(n, subsop(k=2, k+1=2, l)), 0)
      fi
    end:
A:= (n, k)-> `if`(min(n, k)<2, 1, b(max(n, k), [0$min(n, k)])):
seq(seq(A(n, d-n), n=0..d), d=0..14);

Mathematica

b[n_, l_] := b[n, l] = Module[{m=Min[l], k}, If[m>0, b[n-m, l-m], If[n == 0, 1, k=Position[l, 0, 1, 1][[1, 1]]; b[n, ReplacePart[l, k -> 1]] + If[n>1 && k<Length[l] && l[[k+1]] == 0, b[n, ReplacePart[l, {k -> 2, k+1 -> 2}]], 0]]]]; A[n_, k_] := If[Min[n, k]<2, 1, b[Max[n, k], Table[0, {Min[n, k]}]]]; Table[Table[A[n, d-n], {n, 0, d}], {d, 0, 14}] // Flatten (* Jean-François Alcover, Dec 11 2014, after Alois P. Heinz *)

Crossrefs

Columns (or rows) k=0+1,2-10 give: A000012, A000045(n+1), A001045(n+1), A054854, A054855, A063650, A063651, A063652, A063653, A063654.

Main diagonal gives A063443.

Sequence in context: A377007 A327482 A189006 * A219924 A226444 A196929

Adjacent sequences: A245010 A245011 A245012 * A245014 A245015 A245016

Keyword

nonn,tabl

Author

Alois P. Heinz, Sep 16 2014

Status

approved