a(n) = phi(2n+1) / multiplicative order of 2 mod 2n+1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =1a(6) =1a(7) =2a(8) =2a(9) =1a(10) =2a(11) =2a(12) =1a(13) =1a(14) =1a(15) =6a(16) =2a(17) =2a(18) =1a(19) =2a(20) =2a(21) =3a(22) =2a(23) =2a(24) =2a(25) =4a(26) =1a(27) =2a(28) =2a(29) =1