An emirp (prime spelt backwards) is a prime number that results in a different prime when its digits are reversed.[1] This definition excludes the related palindromic primes. Emirps are also called reversible primes.

The sequence of emirps begins 13, 17, 31, 37, 71, 73, 79, 97, 107, 113, 149, 157... (sequence A006567 in OEIS).[1]

All multi-digit, non-repunit permutable primes are emirps.

As of December 2007, the largest known emirp is 1010006+941992101×104999+1, found by Jens Kruse Andersen in October 2007.[2]


1. ^ a b Eric W. Weisstein, Emirp at MathWorld.

2. ^ Rivera, Carlos. "Problems & Puzzles: Puzzle 20.- Reversible Primes". Retrieved on December 17, 2007.

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