a(n) = Sum_{k divides 2^n} S(k), where S is the Kempner function A002034.

Terms

a(0) =1a(1) =3a(2) =7a(3) =11a(4) =17a(5) =25a(6) =33a(7) =41a(8) =51a(9) =63a(10) =75a(11) =89a(12) =105a(13) =121a(14) =137a(15) =153a(16) =171a(17) =191a(18) =211a(19) =233a(20) =257a(21) =281a(22) =305a(23) =331a(24) =359a(25) =387a(26) =417a(27) =449a(28) =481a(29) =513