a(n) = A063776(2*n) + 1.

Terms

a(0) =3a(1) =5a(2) =13a(3) =33a(4) =105a(5) =345a(6) =1173a(7) =4097a(8) =14573a(9) =52433a(10) =190653a(11) =699073a(12) =2581113a(13) =9586985a(14) =35791473a(15) =134217729a(16) =505290273a(17) =1908874585a(18) =7233629133a(19) =27487790721a(20) =104715393913a(21) =399822410105