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 A261964 Chocolate numbers read as a triangle across rows: T(n,k), n >= 1, 1 <= k <= n. 3
 1, 1, 1, 2, 4, 2, 6, 56, 56, 6, 24, 1712, 9408, 1712, 24, 120, 92800, 4948992, 4948992, 92800, 120, 720, 7918592, 6085088256, 63352393728, 6085088256, 7918592, 720, 5040, 984237056, 14782316470272, 2472100837326848, 2472100837326848, 14782316470272, 984237056, 5040 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Given an i X j chocolate bar, let A(i,j) be the number of ways to break it into i*j unit pieces where each break occurs along a grid line. Order matters, and the pieces are distinguishable. Then this sequence lists the values A(i,j) viewed as a triangle and ordered by rows. Row n corresponds to A(i,j), where i+j = n+1. For example, the third row of a triangle is A(3,1)=2, A(2,2)=4, A(1,3)-2. The sequence of factorials, A000142, is a subsequence as A(1,n) = A(n,1) = (n-1)!. For m,n>1, A(m,n) is divisible by 2^(m+n-2). LINKS Caleb Ji, Tanya Khovanova, Robin Park, Angela Song, Chocolate Numbers, arXiv:1509.06093 [math.CO], 2015. Caleb Ji, Tanya Khovanova, Robin Park, Angela Song, Chocolate Numbers, Journal of Integer Sequences, Vol. 19 (2016), #16.1.7. FORMULA T(n,k) = A(n+1-k,k) 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) otherwise. EXAMPLE For n = m = 2, there are two ways for the first break: breaking it horizontally or vertically. After that we need two more breaks that can be done in any order. Thus A(2,2) = 4. Triangle starts: 1, 1, 1, 2, 4, 2, 6, 56, 56, 6, 24, 1712, 9408, 1712, 24, 120, 92800, 4948992, 4948992, 92800, 120, 720, 7918592, 6085088256, 63352393728, 6085088256, 7918592, 720, ... MAPLE A:= proc(m, n) option remember; `if`(min(m, n)=0 or max(m, n)=1, 1,        add(binomial(m*n-2, i*n-1)*A(i, n)*A(m-i, n), i=1..m-1)       +add(binomial(m*n-2, i*m-1)*A(m, i)*A(m, n-i), i=1..n-1))     end: T:= (n, k)-> A(n+1-k, k): seq(seq(T(n, k), k=1..n), n=1..10);  # Alois P. Heinz, Sep 14 2015 MATHEMATICA T[1, 1] = T[2, 1] = T[2, 2] = 1; T[n_, k_] /; 1 <= k <= n := T[n, k] = Sum[Binomial[(n-k+1)*k-2, i*(n-k+1) - 1] * T[n-i, k-i] * T[n-k+i, i], {i, 1, k-1}] + Sum[T[k+i-1, k]*Binomial[ (n-k+1)*k-2, i*k-1] * T[n-i, k], {i, 1, n-k}]; T[_, _] = 0; Table[T[n, k], {n, 1, 10}, {k, 1, n}] // Flatten (* Jean-François Alcover, May 23 2016 *) CROSSREFS Cf. A000142, A257281, A261746, A261747. Sequence in context: A021012 A229460 A154120 * A177847 A296471 A021416 Adjacent sequences:  A261961 A261962 A261963 * A261965 A261966 A261967 KEYWORD nonn,tabl AUTHOR Caleb Ji, Tanya Khovanova, Robin Park, Angela Song, Sep 06 2015 STATUS approved

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