Smallest k such that phi(phi(k)) = 2^n, where phi is the Euler totient function.

Terms

a(0) =5a(1) =11a(2) =17a(3) =41a(4) =85a(5) =137a(6) =257a(7) =641a(8) =1285a(9) =2329a(10) =4369a(11) =10537a(12) =17477a(13) =35209a(14) =65537a(15) =163841a(16) =297109a(17) =557057a(18) =1114129a(19) =2687017a(20) =4491589a(21) =8978569a(22) =16843009a(23) =42009217a(24) =71304257a(25) =143163649a(26) =286331153a(27) =690563369a(28) =1145390149a(29) =2281701377