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

Terms

a(0) =1a(1) =2a(2) =2a(3) =12a(4) =22a(5) =144a(6) =318a(7) =2102a(8) =5120a(9) =34274a(10) =88352a(11) =597002a(12) =1599676a(13) =10879502a(14) =29983958a(15) =204851678a(16) =576914820a(17) =3953960052a(18) =11329537402a(19) =77815428652a(20) =226170428918