Emirps

An emirp is a type of prime number that, when its digits are reversed, still results in a prime number, but the reversed number must be different from the original one. The word "emirp" comes from the word "prime" spelled backwards.

Emirps are part of a special group of numbers called "reversible primes." They are studied in number theory, a branch of mathematics.

 Example 

 13 is an emirp because when reversed, it becomes 31, which is also a prime number.
 17 is an emirp because its reverse, 71, is also prime.

 Properties 

 An emirp always has a minimum of two digits.
 An emirp is not a palindrome (a number that is the same forwards and backwards). For example, 131 is not an emirp because it is the same when reversed.
 The smallest emirp is 13.

 List of emirp pairs 
(13, 31), (17, 71), (37, 73), (79, 97), (107, 701), (113, 311), (149, 941), (157, 751), (179, 971), (199, 991), (337, 733), (347, 743), (359, 953), (389, 983), (709, 907), (739, 937), (769, 967), (1009, 9001), (1021, 1201), (1031, 1301), (1033, 3301), (1061, 1601), (1069, 9601), (1091, 1901), (1097, 7901), (1103, 3011), (1109, 9011), (1151, 1511), (1153, 3511), (1181, 1811), (1193, 3911), (1213, 3121), (1217, 7121), (1223, 3221), (1229, 9221), (1231, 1321), (1237, 7321), (1249, 9421), (1259, 9521), (1279, 9721), (1283, 3821), (1381, 1831), (1399, 9931), (1409, 9041), (1429, 9241), (1439, 9341), (1453, 3541), (1471, 1741), (1487, 7841), (1499, 9941), (1523, 3251), (1559, 9551), (1583, 3851), (1597, 7951), (1619, 9161), (1657, 7561), (1669, 9661), (1723, 3271), (1733, 3371), (1753, 3571), (1789, 9871), (1847, 7481), (1867, 7681), (1879, 9781), (1913, 3191), (1933, 3391), (1949, 9491), (1979, 9791), etc...

Category:Classes of prime numbers