7 Jan
2017
7 Jan
'17
8:58 a.m.
Where should I look for Rich's proof? I don't recall it.
In Bill's 24 Jan 2003 message to math-fun [check the archives], he seems "to have lost the mail with Rich's proof". I will point out however that there is a 1951 reference by Hans-Egon Richert (On permutable primtall) which supposedly proved "that in the range 991 < p < 10^175 the only base 10 permutable primes are repunit primes". If Richard Schroeppel had a proof above that range, it deserves to be better known.