Expansion of ((Product_{k>=1} (1 - x^k)^2/(1 - 4*x^k + x^(2k))) - 1)/2.

Terms

a(0) =0a(1) =1a(2) =5a(3) =18a(4) =71a(5) =260a(6) =990a(7) =3672a(8) =13775a(9) =51343a(10) =191860a(11) =715770a(12) =2672298a(13) =9972092a(14) =37220040a(15) =138903480a(16) =518408351a(17) =1934712530a(18) =7220497115a(19) =26947209762a(20) =100568547820a(21) =375326739216