a(n) = A027113(n, 2n-5).

Terms

a(0) =1a(1) =4a(2) =13a(3) =44a(4) =145a(5) =467a(6) =1475a(7) =4588a(8) =14099a(9) =42919a(10) =129685a(11) =389578a(12) =1164909a(13) =3470513a(14) =10309111a(15) =30551216a(16) =90368547a(17) =266900346a(18) =787325255a(19) =2320267136a(20) =6832609927a(21) =20108081817a(22) =59149096985a(23) =173927024292a(24) =511290023185