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

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =15a(5) =27a(6) =46a(7) =75a(8) =118a(9) =187a(10) =285a(11) =429a(12) =639a(13) =935a(14) =1354a(15) =1945a(16) =2758a(17) =3878a(18) =5417a(19) =7493a(20) =10300a(21) =14070a(22) =19087a(23) =25741a(24) =34542a(25) =46081a(26) =61185a(27) =80869a(28) =106391a(29) =139368