(3/4)*(27*n^2-137*n+180)*n^(n-6)*(2*n-6)!/(n-3)!.

A104003

(3/4)*(27*n^2-137*n+180)*n^(n-6)*(2*n-6)!/(n-3)!.

Terms

    a(0) =6a(1) =306a(2) =29700a(3) =4798080a(4) =1178634240a(5) =412483246560

External references