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 A123521 Triangle read by rows: T(n,k)=number of tilings of a 2 X n grid with k pieces of 1 X 2 tiles (in horizontal position) and 2n-2k pieces of 1 X 1 tiles (0<=k<=n). 3
 1, 1, 1, 2, 1, 1, 4, 4, 1, 6, 11, 6, 1, 1, 8, 22, 24, 9, 1, 10, 37, 62, 46, 12, 1, 1, 12, 56, 128, 148, 80, 16, 1, 14, 79, 230, 367, 314, 130, 20, 1, 1, 16, 106, 376, 771, 920, 610, 200, 25, 1, 18, 137, 574, 1444, 2232, 2083, 1106, 295, 30, 1, 1, 20, 172, 832, 2486, 4744, 5776 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Also the triangle of the coefficients of the squares of the Fibonacci polynomials. Row n has 1+2*floor(n/2) terms. Sum of terms in row n = [fibonacci(n+1)]^2 (A007598). From Michael A. Allen, Jun 24 2020: (Start) T(n,k) is the number of tilings of an n-board (a board with dimensions n X 1) using k (1/2,1/2)-fence tiles and 2(n-k) half-squares (1/2 X 1 pieces, always placed so that the shorter sides are horizontal). A (1/2,1/2)-fence is a tile composed of two 1/2 X 1 pieces separated by a gap of width 1/2. T(n,k) is the (n,(n-k))-th entry of the (1/(1-x^2),x/(1-x)^2) Riordan array. (-1)^(n+k)*T(n,k) is the (n,(n-k))-th entry of the (1/(1-x^2),x/(1+x)^2) Riordan array (A158454). (End) REFERENCES Kenneth Edwards, Michael A. Allen, A new combinatorial interpretation of the Fibonacci numbers squared, Part II, Fib. Q., 58:2 (2020), 169-177. LINKS Kenneth Edwards and Michael A. Allen, New combinatorial interpretations of the Fibonacci numbers squared, golden rectangle numbers, and Jacobsthal numbers using two types of tile, arXiv:2009.04649 [math.CO], 2020. Kenneth Edwards and Michael A. Allen, New combinatorial interpretations of the Fibonacci numbers squared, golden rectangle numbers, and Jacobsthal numbers using two types of tile, JIS 24 (2021) Article 21.3.8. FORMULA G.f.: G=(1-t*z)/[(1+t*z)*(1-z-2*t*z+t^2*z^2)]. G=1/(1-g), where g=z+t^2*z^2+2*t*z^2/(1-t*z) is the g.f. of the indecomposable tilings, i.e., of those that cannot be split vertically into smaller tilings. The row generating polynomials are P[n]=(F[n])^2, where F[n] are the Fibonacci polynomials defined by F=F=1, F[n]=F[n-1]+tF[n-2] for n>=2. They satisfy the recurrence relation P[n]=(1+t)(P[n-1]+t*P[n-2])-t^3*P[n-3]. T(n,k) = T(n-2,k-2)+binomial(2*n-k-1,2*n-2*k-1). - Michael A. Allen, Jun 24 2020 EXAMPLE T(3,1)=4 because the 1 X 2 tile can be placed in any of the four corners of the 2 X 3 grid. Triangle starts: 1; 1; 1,2,1; 1,4,4; 1,6,11,6,1; 1,8,22,24,9; MAPLE G:=(1-t*z)/(1+t*z)/(1-z-2*t*z+t^2*z^2): Gser:=simplify(series(G, z=0, 14)): for n from 0 to 11 do P[n]:=sort(coeff(Gser, z, n)) od: for n from 0 to 11 do seq(coeff(P[n], t, k), k=0..2*floor(n/2)) od; # yields sequence in triangular form MATHEMATICA Block[{T}, T[0, 0] = T[1, 0] = 1; T[n_, k_] := Which[k == 0, 1, k == 1, 2 (n - 1), True, T[n - 2, k - 2] + Binomial[2 n - k - 1, 2 n - 2 k - 1]]; Table[T[n, k], {n, 0, 11}, {k, 0, 2 Floor[n/2]}]] // Flatten (* Michael De Vlieger, Jun 24 2020 *) CROSSREFS Cf. A007598, A158454. Other triangles related to tiling using fences: A059259, A157897, A335964. Sequence in context: A306614 A264336 A322038 * A322115 A294217 A123246 Adjacent sequences:  A123518 A123519 A123520 * A123522 A123523 A123524 KEYWORD nonn,tabf AUTHOR Emeric Deutsch, Oct 16 2006 STATUS approved

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Last modified December 1 04:32 EST 2021. Contains 349426 sequences. (Running on oeis4.)