a(n) = (n!/6) * Sum_{k=0..n-3} 1/k!.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =8a(5) =50a(6) =320a(7) =2275a(8) =18256a(9) =164388a(10) =1644000a(11) =18084165a(12) =217010200a(13) =2821132886a(14) =39495860768a(15) =592437911975