a(n) = Sum_{odd d|n} phi(d)*2^(n/d).

Terms

a(0) =0a(1) =2a(2) =4a(3) =12a(4) =16a(5) =40a(6) =72a(7) =140a(8) =256a(9) =540a(10) =1040a(11) =2068a(12) =4128a(13) =8216a(14) =16408a(15) =32880a(16) =65536a(17) =131104a(18) =262296a(19) =524324a(20) =1048640a(21) =2097480a(22) =4194344a(23) =8388652a(24) =16777728a(25) =33554600a(26) =67108912a(27) =134218836a(28) =268435552a(29) =536870968