Tritriangular numbers: a(n)=binomial(binomial(n,2),2) = n(n + 1)(n - 1)(n - 2)/8.
0, 0, 0, 3, 15, 45, 105, 210, 378, 630, 990, 1485, 2145, 3003, 4095, 5460, 7140, 9180
1 seqfan posts
Sat Aug 6 20:13:07 CEST 2011 [seqfan] Non-Attacking Triangular Board Rooks, guess the recurrence