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

Terms

a(0) =0a(1) =6a(2) =6a(3) =24a(4) =30a(5) =84a(6) =126a(7) =288a(8) =522a(9) =1080a(10) =2046a(11) =4224a(12) =8190a(13) =16548a(14) =32850a(15) =65856a(16) =131070a(17) =262836a(18) =524286a(19) =1049760a(20) =2097438a(21) =4196412a(22) =8388606a(23) =16782048a(24) =33554550a(25) =67117128a(26) =134218782a(27) =268452240a(28) =536870910a(29) =1073777040