a(n) = Sum_{k = 0..4} (n+k)! C(4,k).

Terms

a(0) =23a(1) =65a(2) =261a(3) =1370a(4) =8742a(5) =65304a(6) =557400a(7) =5343120a(8) =56775600a(9) =661933440a(10) =8397406080a(11) =115123680000