a(n) = binomial(n-1,3)*n^(n-4).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =20a(5) =360a(6) =6860a(7) =143360a(8) =3306744a(9) =84000000a(10) =2338460520a(11) =70946979840