Prime Curios!: 8191

8191
(another Prime Pages' Curiosity)

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All Mersenne primes are of the from 2^k - 1, and k must be prime. For 8191, k=13. The case of k=11 (the prime preceding 13) gives the smallest composite Mersenne number, with one of it's factors being 89. If you remove every other digit, you get 89 as well. [Meiburg]

Submitted: 2009-07-03 17:07:36; Last Modified: 2009-07-03 18:51:04.