a(n) = 2*A000129(n) + A000129(n-1) - n.

Terms

a(0) =1a(1) =3a(2) =9a(3) =25a(4) =65a(5) =163a(6) =401a(7) =977a(8) =2369a(9) =5731a(10) =13849a(11) =33449a(12) =80769a(13) =195011a(14) =470817a(15) =1136673a(16) =2744193a(17) =6625091a(18) =15994409a(19) =38613945a(20) =93222337a(21) =225058659a(22) =543339697a(23) =1311738097a(24) =3166815937a(25) =7645370019a(26) =18457556025a(27) =44560482121a(28) =107578520321a(29) =259717522819