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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =19a(5) =64a(6) =219a(7) =777a(8) =2803a(9) =10315a(10) =38496a(11) =145516a(12) =555764a(13) =2142060a(14) =8320207a(15) =32538518a(16) =128012533a(17) =506300507a(18) =2011932479a(19) =8028941336a(20) =32163411045a(21) =129291553211a(22) =521372223648