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

Terms

a(0) =2a(1) =5a(2) =11a(3) =31a(4) =129a(5) =731a(6) =5053a(7) =40335a(8) =362897a(9) =3628819a(10) =39916821a(11) =479001623a(12) =6227020825a(13) =87178291227