s(n+3)/2, where s is A024945.

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =7a(5) =13a(6) =25a(7) =45a(8) =81a(9) =145a(10) =311a(11) =593a(12) =1103a(13) =2137a(14) =4401a(15) =8689a(16) =16769a(17) =32993a(18) =68395a(19) =137141a(20) =270343a(21) =541349a(22) =1119489a(23) =2268541a(24) =4545665a(25) =9161233a(26) =19115279a(27) =39020945a(28) =78883311a(29) =160667153