a(n) = [x^n] Product_{k>=1} ((1 - x^(n*k))/(1 - x^k))^n.

Terms

a(0) =1a(1) =0a(2) =3a(3) =19a(4) =101a(5) =501a(6) =2486a(7) =12398a(8) =62329a(9) =315436a(10) =1605330a(11) =8207552a(12) =42124368a(13) =216903051a(14) =1119974861a(15) =5796944342a(16) =30068145889a(17) =156250892593a(18) =813310723907