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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =6a(5) =11a(6) =29a(7) =71a(8) =179a(9) =505a(10) =1405a(11) =4128a(12) =12639a(13) =39268a(14) =127059a(15) =420281a(16) =1423787a(17) =4955200a(18) =17579398a(19) =63796635a(20) =236161396a(21) =890544028a(22) =3422553065a(23) =13377869976a(24) =53184706291a(25) =214870633711a(26) =881485304157