a(n) = Sum_{d|n, gcd(d, n/d) = 1} (-1)^omega(n/d) * 2^(d-1).

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =15a(5) =27a(6) =63a(7) =127a(8) =255a(9) =495a(10) =1023a(11) =2037a(12) =4095a(13) =8127a(14) =16365a(15) =32767a(16) =65535a(17) =130815a(18) =262143a(19) =524265a(20) =1048509a(21) =2096127a(22) =4194303a(23) =8388477a(24) =16777215a(25) =33550335a(26) =67108863a(27) =134217657a(28) =268435455a(29) =536854005