This number is a prime.
13131 3131313131 3131313131
The smallest palindromic prime greater than 131 formed by alternating 1 and 3. It has a square number of digits (25) and its sum of digits is also a square number (49). [Gallardo]
A prime formed by concatenating thirteen 13's and deleting the last digit. [Avrutin]
Printed from the PrimePages <t5k.org> © G. L. Honaker and Chris K. Caldwell