19

This number is a prime.

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Take the nine pairs (a,b) with a+b=19; take the sum a*b+19 for all these nine pairs; ALL the sums are primes. 19 is the largest prime that will do this. [Bergot]

Submitted: 2011-05-28 17:22:35;   Last Modified: 2011-05-28 21:04:50.
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