Sum_{k, k|n} 2^(k-1) + Sum_{1<=k<=n, gcd(k,n)=1} 2^(k-1).

Terms

a(0) =2a(1) =4a(2) =8a(3) =16a(4) =32a(5) =56a(6) =128a(7) =224a(8) =480a(9) =856a(10) =2048a(11) =3200a(12) =8192a(13) =13656a(14) =29920a(15) =54752a(16) =131072a(17) =202104a(18) =524288a(19) =857952a(20) =1939168a(21) =3495256a(22) =8388608a(23) =12918016a(24) =33013248a(25) =55924056a(26) =124631008a(27) =222655840a(28) =536870912a(29) =809850488