G.f. A(x) satisfies: A(x) = x * Product_{k>=1} 1/(1 - k*A(x^k)).

Terms

a(0) =1a(1) =1a(2) =4a(3) =12a(4) =42a(5) =135a(6) =500a(7) =1797a(8) =6885a(9) =26612a(10) =105561a(11) =423734a(12) =1726531a(13) =7101261a(14) =29486169a(15) =123341520a(16) =519422274a(17) =2199966624a(18) =9365714175a(19) =40052639066a(20) =171985425594a(21) =741214499791