260389232731

This number is a prime.

                                                               26 0389232731

260389232731 = 13579111315 + 246810121416. Note that two terms are concatenations of 8 odd numbers and 8 even numbers. The smaller primes of this type are only 3 = 1 + 2 and 37 = 13 + 24. [Poo Sung]