a(n) = 2^n + ceiling(n/2).

Terms

a(0) =1a(1) =3a(2) =5a(3) =10a(4) =18a(5) =35a(6) =67a(7) =132a(8) =260a(9) =517a(10) =1029a(11) =2054a(12) =4102a(13) =8199a(14) =16391a(15) =32776a(16) =65544a(17) =131081a(18) =262153a(19) =524298a(20) =1048586a(21) =2097163a(22) =4194315a(23) =8388620a(24) =16777228a(25) =33554445a(26) =67108877a(27) =134217742a(28) =268435470a(29) =536870927