G.f.: 1 + Sum_{n>=1} x^n * exp( Sum_{k>=1} binomial(2*n*k-1, n*k) * x^(n*k)/k ).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =9a(5) =15a(6) =75a(7) =133a(8) =676a(9) =1712a(10) =7295a(11) =16797a(12) =100889a(13) =208013a(14) =1083061a(15) =3186268a(16) =14634359a(17) =35357671a(18) =209715154a(19) =477638701a(20) =2679305455a(21) =7638371497a(22) =35224117709a(23) =91482563641a(24) =568102780247