757

This number is a prime.

757 is the smallest palindromic prime of the form 3^(2n) + 3^n + 1 for positive integer n (achieved at n = 3). From this form, it is visible that 757 is also a palindrome in base 3 (1001001) and base 27 (111), since 27 = 3^3. Coincidentally, it is also a palindrome in base 21, written as 1F1 (where F = 15). [Ahmed]