G.f.: Sum_{k>=0} x^k * Product_{j=1..4*k} (1 + x^j).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =7a(6) =9a(7) =12a(8) =16a(9) =20a(10) =26a(11) =33a(12) =41a(13) =52a(14) =65a(15) =81a(16) =99a(17) =121a(18) =147a(19) =177a(20) =214a(21) =255a(22) =304a(23) =362a(24) =429a(25) =507a(26) =596a(27) =700a(28) =820a(29) =959