a(n) = Sum_{p|n, p prime} (n-p)!.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =1a(5) =30a(6) =1a(7) =720a(8) =720a(9) =40440a(10) =1a(11) =3991680a(12) =1a(13) =479006640a(14) =482630400a(15) =87178291200a(16) =1a(18) =1a(22) =1