G.f.: Product_{i>=1, j>=1} 1/(1 - x^(i*j))^(i*j).

Terms

a(0) =1a(1) =1a(2) =5a(3) =11a(4) =33a(5) =67a(6) =180a(7) =366a(8) =871a(9) =1782a(10) =3927a(11) =7885a(12) =16637a(13) =32763a(14) =66469a(15) =128938a(16) =253871a(17) =484034a(18) =930959a(19) =1747304a(20) =3292730a(21) =6092664a(22) =11282364a(23) =20596790a(24) =37568653a(25) =67736175a(26) =121886533a(27) =217261372a(28) =386216073a(29) =681119439