7667

This number is a composite.

The only 4-digit 2-sphenic palindrome that is transformed into another 2-sphenic palindrome upon the insertion of a single 0 in the middle, i.e., 7667 = 11 × 17 × 41 and 76067 = 29 × 43 × 61. [Loungrides]

Reversal(2^7667-1) is the smallest titanic prime of the form reversal(2^n-1). Note that 7667 is the only known multidigit palindromic number n, where reversal(2^n-1) is prime. Note that it is prime for the values n = 2, 3, 5, 53, 189, 293, 1107, 2181, 2695, 2871, 7667. [Sariyar]