"The poet only asks to get his head into the heavens. It is the logician who seeks to get the heavens into his head. And it is his head that splits." G.K. Chesterton

Sunday, May 9, 2010

Arithmetic sequences in digits of primes

Here's a fun fact about prime numbers: there are only 5 prime numbers, whose digits (there are bound to be more if we consider positive integers) express an arithmnetic sequence with common difference 1. They are 23, 67, 89, 4567 and 23456789.

123456789 is not a prime.

By exhaustion :)

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