Expansion of Product_{k>=0} ((1+x^(3*k+1))/(1-x^(3*k+1)))^2.

Terms

a(0) =1a(1) =4a(2) =8a(3) =12a(4) =20a(5) =36a(6) =56a(7) =80a(8) =120a(9) =180a(10) =252a(11) =348a(12) =492a(13) =680a(14) =912a(15) =1228a(16) =1652a(17) =2180a(18) =2856a(19) =3744a(20) =4860a(21) =6256a(22) =8044a(23) =10284a(24) =13048a(25) =16520a(26) =20848a(27) =26140a(28) =32672a(29) =40756