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 A257281 Chocolate square numbers. 3
 1, 1, 4, 9408, 63352393728, 3947339798331748515840, 5732998662938820430255187886059028480, 417673987760293241182652126617960927525362518081132298240 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Given an n X n chocolate bar, a(n) is the number of ways to break it into n^2 unit pieces where each break occurs along a grid line. Order matters, and the pieces are distinguishable. a(n) is divisible by 2^(2n-2). LINKS Caleb Ji, Tanya Khovanova, Robin Park, Angela Song, Chocolate Numbers, arXiv:1509.06093 [math.CO], (21-September-2015). Caleb Ji, Tanya Khovanova, Robin Park, Angela Song, Chocolate Numbers, Journal of Integer Sequences, Vol. 19 (2016), #16.1.7. FORMULA a(n) = A(n,n) with A(m,n)=1 for max(m,n)<2 and A(m,n) = Sum_{i=1..m-1} C(m*n-2,i*n-1) *A(i,n) *A(m-i,n) + Sum_{i=1..n-1} C(m*n-2,i*m-1) *A(m,i) *A(m,n-i) else. EXAMPLE For n = 2, there are two ways for the first break: breaking it horizontally or vertically. After that we need two more breaks, which can be done in either order. Thus a(2) = 4. MATHEMATICA A[m_, n_] := A[m, n] = If[Max[m, n]<2, 1, Sum[A[i, n] Binomial[m n - 2, i n - 1] A[m-i, n], {i, 1, m-1}]] + Sum[A[m, i] Binomial[m n - 2, i m - 1] A[m, n-i], {i, 1, n-1}]; a[n_] := A[n, n]; Table[a[n], {n, 0, 7}] (* Jean-François Alcover, Dec 12 2018 *) CROSSREFS Cf. A261746, A261747, A261964. Sequence in context: A072724 A116271 A274551 * A201392 A058417 A191592 Adjacent sequences:  A257278 A257279 A257280 * A257282 A257283 A257284 KEYWORD nonn AUTHOR Caleb Ji, Tanya Khovanova, Robin Park, Angela Song, Apr 19 2015 STATUS approved

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Last modified September 24 17:09 EDT 2020. Contains 337321 sequences. (Running on oeis4.)