757

This number is a prime.

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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]

757 is the smallest multidigit palindromic prime p = Pₙ for which the symmetric concatenation n||p||rev(n) yields a palindromic prime: 134||757||431 = 134757431. [Ahmed]