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

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =7a(5) =20a(6) =43a(7) =110a(8) =262a(9) =674a(10) =1684a(11) =4397a(12) =11320a(13) =29938a(14) =78641a(15) =210044a(16) =559724a(17) =1507563a(18) =4060585a(19) =11016027a(20) =29919220a(21) =81673846a(22) =223307300a(23) =612851316a(24) =1684816018a(25) =4645243490a(26) =12829177587a(27) =35513736868a(28) =98465916370a(29) =273531234027