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

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =15a(5) =29a(6) =51a(7) =87a(8) =143a(9) =227a(10) =353a(11) =537a(12) =803a(13) =1185a(14) =1727a(15) =2489a(16) =3551a(17) =5021a(18) =7039a(19) =9791a(20) =13521a(21) =18541a(22) =25261a(23) =34207a(24) =46051a(25) =61655a(26) =82113a(27) =108815a(28) =143517a(29) =188433