G.f. A(x) satisfies 2 = Sum_{n=-oo..+oo} x^(4*n) * (1 - x^n)^(4*n) * A(x)^n.

Terms

a(0) =1a(1) =4a(2) =10a(3) =20a(4) =36a(5) =60a(6) =94a(7) =140a(8) =204a(9) =292a(10) =474a(11) =756a(12) =1556a(13) =2600a(14) =5612a(15) =9404a(16) =21174a(17) =39896a(18) =95446a(19) =204960a(20) =486168a(21) =1076000a(22) =2392306a(23) =5215772a(24) =11042630a(25) =24216104a(26) =51067130a(27) =115069352a(28) =246871472a(29) =563237900