29587

This number is a prime.

The sum of all the primes that are concatenated from two successive double-digit primes, i.e., 3137+5347+5953+6761+8389. [Loungrides]

Append or prepend any of the digits 1, 3, 7, or 9, and 29587 will remain prime. This is the smallest prime with this property. [Henriksen]