a(1) = 1; a(n+1) = n!*Sum_{k|n} a(k)/k!.

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =45a(5) =165a(6) =1605a(7) =6645a(8) =82245a(9) =626565a(10) =7430565a(11) =47347365a(12) =1294747365a(13) =7521768165a(14) =166051339365