G.f. satisfies A(x) = 1 + x*A(x)^2*A(x^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =18a(5) =59a(6) =198a(7) =690a(8) =2450a(9) =8878a(10) =32632a(11) =121518a(12) =457262a(13) =1736526a(14) =6646340a(15) =25613086a(16) =99298674a(17) =387021728a(18) =1515594560a(19) =5960406102a(20) =23530528512a(21) =93216984177a(22) =370450977206