G.f.: Product_{n=-oo..+oo} ( 1 + x^n*(1 - x^n)^n ).

Terms

a(0) =-2a(1) =-4a(2) =-6a(3) =-12a(4) =-14a(5) =-22a(6) =-30a(7) =-40a(8) =-38a(9) =-44a(10) =-64a(11) =-54a(12) =-40a(13) =16a(14) =12a(15) =54a(16) =94a(17) =248a(18) =370a(19) =672a(20) =754a(21) =932a(22) =1112a(23) =1360a(24) =2388a(25) =2684a(26) =3508a(27) =4388a(28) =4452a(29) =4240