# What is an emirp?« Back to Questions List

An emirp (prime spelled backwards) is a prime number that results in a different prime when its digits are reversed. (This definition excludes the related palindromic primes(A palindromic number or numeral palindrome is a number that remains the same when its digits are reversed. The first palindromic numbers (in decimal) are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191... A palindromic prime (sometimes called a palprime) is a prime number that is also a palindromic number.The first few decimal palindromic primes are:2, 3, 5, 7, 11, 101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929, … The term reversible prime may be used to mean the same as emirp, but may also, ambiguously, include the palindromic primes.) Hence, the sequence of emirps begins 13, 17, 31, 37, 71, 73, 79, 97, 107, 113, 149, 157... All non-palindromic permutable primes are emirps. As of November 2009, the largest known emirp is 1010006+941992101×104999+1, found by Jens Kruse Andersen in October 2007. The smallest emirp.