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

Terms

a(0) =2a(1) =3a(2) =4a(3) =7a(4) =10a(5) =18a(6) =30a(7) =54a(8) =94a(9) =176a(10) =316a(11) =591a(12) =1096a(13) =2058a(14) =3856a(15) =7301a(16) =13798a(17) =26244a(18) =49940a(19) =95373a(20) =182362a(21) =349626a(22) =671092a(23) =1290714a(24) =2485534a(25) =4793790a(26) =9256396a(27) =17896284a(28) =34636834a(29) =67109898