a(n) = floor(exp(1/13)*n!).

Terms

a(0) =1a(1) =2a(2) =6a(3) =25a(4) =129a(5) =777a(6) =5442a(7) =43543a(8) =391895a(9) =3918955a(10) =43108507a(11) =517302088a(12) =6724927152a(13) =94148980136