a(n) = Sum_{d|n} phi(n/d)^2*2^(d+1).

Terms

a(0) =0a(1) =4a(2) =12a(3) =32a(4) =56a(5) =128a(6) =192a(7) =400a(8) =640a(9) =1232a(10) =2304a(11) =4496a(12) =8608a(13) =16960a(14) =33456a(15) =66304a(16) =132096a(17) =263168a(18) =526320a(19) =1049872a(20) =2100352a(21) =4196480a(22) =8393904a(23) =16779152a(24) =33565952a(25) =67111488a(26) =134235840a(27) =268441424a(28) =536906720a(29) =1073744960