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Old 2003-04-13, 23:49   #6
Jan 2003
far from M40

53 Posts

For another question I just found an answer on Chris Caldwell's PrimeGlossary: do all palindromic primes have a p^n number of digits? - No!
For base-10, I tested it up to 2^31 - 1, which gave 1, 2, 3, 5 and 7 digits.
For twin palindromic primes (BTW, I think 'palindromic prime pair' could be a better name to avoid confusion with palindromic primes that are also prime twins, besides it's a nice anaphora.:)) this isn't the case, either. Counter example: 1009 and 9001.


P.S.: If I got it right, in Chris Caldwell's PrimeGlossary, they are called 'invertable primes'.
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