Coefficient of x^(2*n) in (-1 + Product_{k>=1} (1 - x^k))^n.

Terms

a(0) =1a(1) =-1a(2) =1a(3) =-1a(4) =-3a(5) =19a(6) =-65a(7) =181a(8) =-419a(9) =755a(10) =-749a(11) =-1530a(12) =12255a(13) =-47477a(14) =141065a(15) =-343526a(16) =660941a(17) =-770917a(18) =-911369a(19) =9721976a(20) =-40135713a(21) =124134772a(22) =-313463842a(23) =631382751a(24) =-824406065a(25) =-492101356a(26) =8192253811a(27) =-35948431288a(28) =115087580857a(29) =-299576625051