a(n) is the next Ulam number (A002858) after 2^(n-1).

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =11a(5) =18a(6) =36a(7) =69a(8) =131a(9) =258a(10) =522a(11) =1025a(12) =2054a(13) =4101a(14) =8194a(15) =16394a(16) =32817a(17) =65542a(18) =131085a(19) =262183a(20) =524313a(21) =1048588a(22) =2097164a(23) =4194310a(24) =8388624a(25) =16777218a(26) =33554433a(27) =67108881a(28) =134217730a(29) =268435473