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

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =6a(6) =8a(7) =11a(8) =14a(9) =18a(10) =23a(11) =30a(12) =38a(13) =47a(14) =58a(15) =71a(16) =87a(17) =106a(18) =128a(19) =154a(20) =185a(21) =221a(22) =263a(23) =313a(24) =370a(25) =437a(26) =514a(27) =603a(28) =705a(29) =822