a(n) = binomial(n-1,4)*n^(n-5).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =30a(6) =735a(7) =17920a(8) =459270a(9) =12600000a(10) =372027810a(11) =11824496640a(12) =403786706895