a(n) = 3*n! + 1.

Terms

a(0) =4a(1) =4a(2) =7a(3) =19a(4) =73a(5) =361a(6) =2161a(7) =15121a(8) =120961a(9) =1088641a(10) =10886401a(11) =119750401a(12) =1437004801a(13) =18681062401a(14) =261534873601