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

Terms

a(0) =0a(1) =2a(2) =6a(3) =12a(4) =24a(5) =40a(6) =84a(7) =140a(8) =288a(9) =540a(10) =1080a(11) =2068a(12) =4224a(13) =8216a(14) =16548a(15) =32880a(16) =65856a(17) =131104a(18) =262836a(19) =524324a(20) =1049760a(21) =2097480a(22) =4196412a(23) =8388652a(24) =16782048a(25) =33554600a(26) =67117128a(27) =134218836a(28) =268452240a(29) =536870968