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

Terms

a(0) =2a(1) =8a(2) =12a(3) =32a(4) =40a(5) =96a(6) =140a(7) =320a(8) =540a(9) =1120a(10) =2068a(11) =4320a(12) =8216a(13) =16688a(14) =32880a(15) =66176a(16) =131104a(17) =263376a(18) =524324a(19) =1050880a(20) =2097480a(21) =4198480a(22) =8388652a(23) =16786368a(24) =33554600a(25) =67125344a(26) =134218836a(27) =268468928a(28) =536870968a(29) =1073809920