a(n) = (2*n+7)!!/7!!, related to A001147 (odd double factorials).

A051581

a(n) = (2*n+7)!!/7!!, related to A001147 (odd double factorials).

Terms

    a(0) =1a(1) =9a(2) =99a(3) =1287a(4) =19305a(5) =328185a(6) =6235515a(7) =130945815a(8) =3011753745a(9) =75293843625

External references