19

This number is a prime.

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Consider i + j = 19 for 0 < i, j < 19 and i * j + 19 is prime for ALL cases: 1*18+19=37, 2*17+19=53, 3*16+19=67, 4*15+19=79, 5*14+19=89, 6*13+19=97, 7*12+19=103, 8*11+19=107, 9*10+19=109. This also works for 2 and 7. Can it work for a prime greater than 19? [Bergot]

Submitted: 2018-05-28 18:03:25; Last Modified: 2018-05-28 18:07:54.