Expansion of Product_{k>=1} (1 + x^k + x^(3*k)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =2a(5) =4a(6) =6a(7) =7a(8) =8a(9) =13a(10) =16a(11) =18a(12) =26a(13) =29a(14) =38a(15) =49a(16) =58a(17) =68a(18) =90a(19) =101a(20) =125a(21) =156a(22) =181a(23) =214a(24) =263a(25) =304a(26) =358a(27) =435a(28) =505a(29) =589