G.f.: (1-2*x^2)/(1-2*x-5*x^2+9*x^3).

Terms

a(0) =1a(1) =2a(2) =7a(3) =15a(4) =47a(5) =106a(6) =312a(7) =731a(8) =2068a(9) =4983a(10) =13727a(11) =33757a(12) =91302a(13) =227846a(14) =608389a(15) =1534290a(16) =4059911a(17) =10315771a(18) =27122487a(19) =69284630a(20) =181339756a(21) =465000279a(22) =1213137668a(23) =3119218927a(24) =8119123683a(25) =20916102989a(26) =54354854050a(27) =140218109898a(28) =363965563145a(29) =939827989330