Re: [math-fun] question

David Wilson wrote:

x == 1 (mod phi(x)) ==> x prime? (x >= 2)

This was conjectured by D.H. Lehmer in 1932 and remains open. There are many references at B37 in Guy's _Unsolved Problems in Number Theory_. Lehmer noted in his original article that the problem was similar to that of odd perfect numbers, and since then the published results have had the same flavor: a counterexample must have a certain form, must be large, must have many prime divisors, etc. -- Fred W. Helenius fredh@ix.netcom.com