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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =4a(6) =7a(7) =16a(8) =39a(9) =93a(10) =246a(11) =671a(12) =1884a(13) =5578a(14) =16887a(15) =52854a(16) =170649a(17) =563703a(18) =1914366a(19) =6649798a(20) =23610987a(21) =85689987a(22) =317054427a(23) =1196183592a(24) =4595744763a(25) =17965311672a(26) =71426213637a(27) =288535755417