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

Terms

a(0) =1a(1) =3a(2) =7a(3) =21a(4) =61a(5) =179a(6) =527a(7) =1561a(8) =4617a(9) =13667a(10) =40455a(11) =119765a(12) =354541a(13) =1049587a(14) =3107183a(15) =9198529a(16) =27231329a(17) =80615763a(18) =238655191a(19) =706515909a(20) =2091572621a(21) =6191900707a(22) =18330529343a(23) =54265778345a(24) =160648643833a(25) =475584938515