a(n) = Sum_{d|n} (2^(n-d)).

Terms

a(0) =1a(1) =3a(2) =5a(3) =13a(4) =17a(5) =57a(6) =65a(7) =209a(8) =321a(9) =801a(10) =1025a(11) =3905a(12) =4097a(13) =12417a(14) =21505a(15) =53505a(16) =65537a(17) =233985a(18) =262145a(19) =885761a(20) =1327105a(21) =3147777a(22) =4194305a(23) =16060417a(24) =17825793a(25) =50339841a(26) =84148225a(27) =220217345a(28) =268435457a(29) =990937089