G.f.: Product_{k>=1, j>=1} (1 + x^(k*j))^2.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =24a(5) =48a(6) =94a(7) =172a(8) =310a(9) =550a(10) =946a(11) =1602a(12) =2679a(13) =4394a(14) =7123a(15) =11424a(16) =18082a(17) =28344a(18) =44039a(19) =67754a(20) =103412a(21) =156660a(22) =235489a(23) =351602a(24) =521650a(25) =768998a(26) =1127100a(27) =1642946a(28) =2381929a(29) =3436028