OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..66
Paul Barry, Jacobsthal Decompositions of Pascal's Triangle, Ternary Trees, and Alternating Sign Matrices, Journal of Integer Sequences, 19, 2016, #16.3.5.
J. de Gier, Loops, matchings and alternating-sign matrices, arXiv:math/0211285 [math.CO], 2002-2003.
Heuer, Dylan, Chelsey Morrow, Ben Noteboom, Sara Solhjem, Jessica Striker, and Corey Vorland. "Chained permutations and alternating sign matrices - Inspired by three-person chess." Discrete Mathematics 340, no. 12 (2017): 2732-2752. Also arXiv:1611.03387.
G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv:math/0008184 [math.CO], 2001.
FORMULA
a(n) = A049503(n)*Product_{k=0..n-1} (3*k+2)/(3*k+1). - Seiichi Manyama, Jul 29 2018
a(n) ~ exp(1/18) * Gamma(1/3)^(2/3) * n^(1/18) * 3^(3*n^2 + 1/9) / (A^(2/3) * Pi^(1/3) * 2^(4*n^2 + 1/6)), where A is the Glaisher-Kinkelin constant A074962. - Vaclav Kotesovec, Jan 26 2020
MATHEMATICA
a[n_] := Product[(3k+1)(3k+2)(3k)!^2/(n+k)!^2, {k, 0, n-1}];
Table[a[n], {n, 0, 13}] (* Jean-François Alcover, Sep 01 2018, after Seiichi Manyama *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Feb 04 2001
STATUS
approved