G.f. satisfies: A(x) = Sum_{n>=0} x^n * A(x)^(n*(n-1)/2).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =15a(6) =50a(7) =181a(8) =698a(9) =2837a(10) =12062a(11) =53374a(12) =244923a(13) =1162536a(14) =5697119a(15) =28786266a(16) =149814059a(17) =802436166a(18) =4420515689a(19) =25031466730a(20) =145616087486a(21) =869760092469