a(n) = n! + (2*n-1)!/(n-1)!.

A226730

a(n) = n! + (2*n-1)!/(n-1)!.

Terms

    a(0) =2a(1) =8a(2) =66a(3) =864a(4) =15240a(5) =333360a(6) =8653680a(7) =259499520a(8) =8821975680a(9) =335224915200

External references