20

This number is a composite.

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The only number n < 1000, such that subtracting from it each of the first seven powers of 3, then all absolute differences that are obtained, 20-3^0, 20-3^1, …, 20-3^6 are primes, i.e., 19, 17, 11, 7, 61, 223, 709. [Loungrides]

Submitted: 2013-06-15 09:40:40;   Last Modified: 2018-05-09 05:45:28.
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