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

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =23a(5) =62a(6) =179a(7) =571a(8) =1888a(9) =6309a(10) =21114a(11) =71387a(12) =245162a(13) =854703a(14) =3010602a(15) =10673814a(16) =38036229a(17) =136250135a(18) =490696565a(19) =1776089734a(20) =6456234450a(21) =23554296293a(22) =86210280655a(23) =316481218498