G.f.: Sum_{k>=0} x^k * Product_{j=1..3*k} (1 + x^j)/(1 - x^j).

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =15a(5) =27a(6) =47a(7) =79a(8) =127a(9) =199a(10) =307a(11) =465a(12) =695a(13) =1025a(14) =1493a(15) =2151a(16) =3069a(17) =4337a(18) =6075a(19) =8441a(20) =11639a(21) =15933a(22) =21667a(23) =29281a(24) =39337a(25) =52555a(26) =69849a(27) =92375a(28) =121595a(29) =159347