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

Terms

a(0) =1a(1) =3a(2) =9a(3) =23a(4) =57a(5) =139a(6) =337a(7) =815a(8) =1969a(9) =4755a(10) =11481a(11) =27719a(12) =66921a(13) =161563a(14) =390049a(15) =941663a(16) =2273377a(17) =5488419a(18) =13250217a(19) =31988855a(20) =77227929a(21) =186444715a(22) =450117361a(23) =1086679439a(24) =2623476241a(25) =6333631923a(26) =15290740089a(27) =36915112103a(28) =89120964297a(29) =215157040699