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A054854
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Number of ways to tile a 4 X n region with 1 X 1 and 2 X 2 tiles.
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16
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1, 1, 5, 11, 35, 93, 269, 747, 2115, 5933, 16717, 47003, 132291, 372157, 1047181, 2946251, 8289731, 23323853, 65624397, 184640891, 519507267, 1461688413, 4112616845, 11571284395, 32557042499, 91602704493, 257733967693, 725161963867
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OFFSET
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0,3
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LINKS
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D. Abadie, J. Andreoli, S. Egan, T. Reddy, D. Xiong, Y. Zhao, and A. Zhu, On the Number of Tilings of a 4-By-N Rectangle with 1-By-1 and 2-By-2 Squares, Girls' Angle Bulletin, Vol. 15, No. 2 (2021), 8-12.
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FORMULA
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a(n) = a(n-1)+4*a(n-2)+2*( a(n-3)+a(n-4)+...+a(0) ).
a(n) = 2*a(n-1)+3*a(n-2)-2*a(n-3). [See proofs in Mathar (a transfer matrix approach) and in Abadie et al.(direct proof).] - Keith Schneider (kschneid(AT)bulldog.unca.edu), Apr 02 2006
a(n) = Term (2,2) of matrix [5,1,1; 1,1,0; 1,0,1/2]*[2,1,0; 3,0,1; -2,0,0]^n. - Alois P. Heinz, May 18 2008
a(n) = F(n+1)^2 + Sum_{k=1..n-1} F(k)^2 * a(n-k-1), for n >= 0, where F(k) = A000045(k) (Fibonacci numbers), see Abadie, et al. - Richard S. Chang, Jan 21 2022
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EXAMPLE
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a(2) = 5 as there is one tiling of a 4x2 region with only 1 X 1 tiles, 3 tilings with exactly one 2 X 2 tile and one tiling consisting of two 2 X 2 tiles.
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MAPLE
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A:= Matrix([[5, 1, 1], [1, 1, 0], [1, 0, 1/2]]); M:= Matrix([[2, 1, 0], [3, 0, 1], [ -2, 0, 0]]): a:= n->(A.M^n)[2, 2]: seq(a(n), n=0..50); # Alois P. Heinz, May 18 2008
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MATHEMATICA
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f[{A_, B_}] := Module[{til = A, basic = B}, {Flatten[Append[til, ListConvolve[A, B]]], AppendTo[basic, 2]}]; NumOfTilings[n_] := Nest[f, {{1, 1}, {1, 4}}, n - 2][[1]] NumOfTilings[30]
(* Second program: *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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Silvia Heubach (silvi(AT)cine.net), Apr 21 2000
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STATUS
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approved
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