a(n) = phi(phi(n)), where phi is the Euler totient function.

Terms

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