Expansion of Product_{k>=1} ((1 + x^k)/(1 - x^k))^(sigma_2(k)).

Terms

a(0) =1a(1) =2a(2) =12a(3) =42a(4) =154a(5) =498a(6) =1640a(7) =4990a(8) =15092a(9) =43840a(10) =125220a(11) =348478a(12) =954294a(13) =2561714a(14) =6776404a(15) =17644494a(16) =45338734a(17) =114971434a(18) =288148860a(19) =713968998a(20) =1750662814a(21) =4249685398a(22) =10219662844a(23) =24356466418a(24) =57558783492a(25) =134922807056a(26) =313842321696a(27) =724651728916