OFFSET
0,8
LINKS
I. Dolinka, J. East, A. Evangelou, D. FitzGerald, N. Ham, et al., Enumeration of idempotents in diagram semigroups and algebras, arXiv preprint arXiv:1408.2021 [math.GR], 2014.
FORMULA
Conjecture: T(n,k) = (n+k-1)!!/(2k-1)!! for n+k even, T(n,k) = 0 otherwise. - Jean-François Alcover, Feb 11 2019
EXAMPLE
Triangle begins:
1,
0, 1,
1, 0, 1,
0, 3, 0, 1,
3, 0, 5, 0, 1,
0, 15, 0, 7, 0, 1,
15, 0, 35, 0, 9, 0, 1,
0, 105, 0, 63, 0, 11, 0, 1,
105, 0, 315, 0, 99, 0, 13, 0, 1,
0, 945, 0, 693, 0, 143, 0, 15, 0, 1,
945, 0, 3465, 0, 1287, 0, 195, 0, 17, 0, 1,
...
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
N. J. A. Sloane, Mar 14 2015
STATUS
approved