a(n) = Product_{d|n} Stirling2(n,d).

Terms

a(0) =1a(1) =1a(2) =1a(3) =7a(4) =1a(5) =2790a(6) =1a(7) =216027a(8) =3025a(9) =21730275a(10) =1a(12) =1a(13) =404056132480a(16) =1a(18) =1