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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =22a(5) =91a(6) =408a(7) =1939a(8) =9635a(9) =49614a(10) =263140a(11) =1431301a(12) =7959568a(13) =45152340a(14) =260847526a(15) =1532825675a(16) =9154581802a(17) =55537885743a(18) =342147577227