Emirps, which is Prime spelled backwards, are prime numbers that are "reversible". When their digits are reversed, they can form a different prime number.
This excludes Palindromic Primes, since the result has to be different than the original number.
- 13 is the first emirp. When reversed, it becomes 31, which is also a prime number.
- 17 is the second emirp. When reversed, it becomes 71, which is also a prime number.
- Since 13 is an emirp, 31 is also an emirp, since the digits becomes 13 when reversed.