[math-fun] permutable primes redux

Despite computer searches, 991 was the last known value of A003459 for improbably long, prompting NJAS to cajole math-fun for more. Rich then found his startling proof that all the elements past 991 were repunits, so next comes (10^19 - 1)/9. In retrospect, R(19) and R(23) should have been found previously by searching. Why weren't they? Bad algorithms? Unavailability of bignums? Programming was more tedious then. See A258706, the condensed version of A003459. Now the tedious part is deciphering the Mathematica. --rwg