G.f.: exp( Sum_{n>=1} x^n/n * Product_{k>=1} (1 + x^(n*k)*(1 + x^n)^k) ).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =9a(5) =20a(6) =45a(7) =97a(8) =217a(9) =476a(10) =1043a(11) =2256a(12) =4890a(13) =10540a(14) =22695a(15) =48614a(16) =103856a(17) =221103a(18) =469738a(19) =995299a(20) =2104514a(21) =4439410a(22) =9345471a(23) =19631897a(24) =41162937a(25) =86148416a(26) =179987656a(27) =375411910a(28) =781773332a(29) =1625473202