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

Terms

a(0) =2a(1) =3a(2) =10a(3) =54a(4) =408a(5) =3960a(6) =46800a(7) =650160a(8) =10362240a(9) =186157440a(10) =3719520000a(11) =81789523200