G.f.: x * Product_{k>=1} (1 + k*x^k)^a(k).

Terms

a(0) =1a(1) =1a(2) =2a(3) =8a(4) =38a(5) =234a(6) =1679a(7) =13802a(8) =127155a(9) =1297619a(10) =14516296a(11) =176640311a(12) =2322876382a(13) =32831464503a(14) =496399943530