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

Terms

a(0) =0a(1) =2a(2) =6a(3) =16a(4) =28a(5) =64a(6) =96a(7) =200a(8) =320a(9) =616a(10) =1152a(11) =2248a(12) =4304a(13) =8480a(14) =16728a(15) =33152a(16) =66048a(17) =131584a(18) =263160a(19) =524936a(20) =1050176a(21) =2098240a(22) =4196952a(23) =8389576a(24) =16782976a(25) =33555744a(26) =67117920a(27) =134220712a(28) =268453360a(29) =536872480