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

Terms

a(0) =1a(1) =0a(2) =1a(3) =3a(4) =10a(5) =28a(6) =79a(7) =216a(8) =603a(9) =1702a(10) =4933a(11) =14620a(12) =44287a(13) =136352a(14) =424858a(15) =1334162a(16) =4211572a(17) =13344072a(18) =42412667a(19) =135217722a(20) =432483522a(21) =1387929369a(22) =4469341807a(23) =14439523193a(24) =46795072968a(25) =152076428228a(26) =495460089510