a(n) = Sum_{k=1..n} 2^(k/gcd(n,k) - 1).

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =16a(5) =22a(6) =64a(7) =92a(8) =223a(9) =342a(10) =1024a(11) =1132a(12) =4096a(13) =5462a(14) =13534a(15) =21937a(16) =65536a(17) =70978a(18) =262144a(19) =333472a(20) =890590a(21) =1398102a(22) =4194304a(23) =4528402a(24) =16236031a(25) =22369622a(26) =57522106a(27) =88435312a(28) =268435456a(29) =272976502