OFFSET
0,3
COMMENTS
a(n) is an upper bound of the number of vertices of the polytope of the n X n X n stochastic tensors, or equivalently, of the number of Latin squares of order n, or equivalently, of the number of n X n X n line-stochastic (0,1)-tensors (see Zhang et al.).
LINKS
Fuzhen Zhang and Xiao-Dong Zhang, Enumerating extreme points of the polytopes of stochastic tensors: an optimization approach, Optimization, 69:4, 729-741, (2020). arXiv:2008.04655 [math.CO], 2020. See p. 6.
Fuzhen Zhang and Xiao-Dong Zhang, Comparison of the upper bounds for the extreme points of the polytopes of line-stochastic tensors, arXiv:2110.12337 [math.CO], 2021. See p. 4.
FORMULA
a(n) = binomial(n^3, n^2)*2F1([1, n^2-n^3], [1+n^2], -1) - binomial(n^3, 2-3*n+3*n^2)*2F1([1, 2-3*n+3*n^2-n^3], [3(1-n+n^2)], -1), where 2F1 is the hypergeometric function.
a(n) ~ exp(3*n^2 - 9*n/2 + 3) * n^(3*n*(n-1)) / (sqrt(2*Pi) * 3^(3*n^2 - 3*n + 3/2)). - Vaclav Kotesovec, Dec 05 2021
MATHEMATICA
a[n_]:=Sum[Binomial[n^3, k], {k, n^2, 3n^2-3n+1}]; Array[a, 8, 0]
CROSSREFS
KEYWORD
nonn
AUTHOR
Stefano Spezia, Nov 20 2021
STATUS
approved