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

A002690

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

Terms

    a(0) =1a(1) =4a(2) =36a(3) =480a(4) =8400a(5) =181440a(6) =4656960a(7) =138378240a(8) =4670265600a(9) =176432256000

External references