

A261747


Chocolate2 numbers.


3



1, 1, 4, 56, 1712, 92800, 7918592, 984237056, 168662855680, 38238313152512, 11106033743298560, 4026844843819663360, 1784377436257886142464, 949324216111786046259200, 597340801661667138076672000, 438858704839955952346364641280
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OFFSET

0,3


COMMENTS

Given a 2byn chocolate bar, a(n) is the number of ways to break it into 2n unit pieces where each break occurs along a gridline. Order matters, and the pieces are distinguishable.
For n>1, a(n) is divisible by 2^n.


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

a(n) = A(n,2) with A(m,n)=1 for max(m,n)<2 and A(m,n) = Sum_{i=1..m1} C(m*n2,i*n1) *A(i,n) *A(mi,n) + Sum_{i=1..n1} C(m*n2,i*m1) *A(m,i) *A(m,ni) 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 that can be done in any order. Thus a(2) = 4.


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



