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121 (another Prime Pages' Curiosity) |
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121 is the only known square of the form 1 + p + p2 + p3 + p4, where p is prime. Every number greater than 121 is the sum of distinct primes of the form 4n + 1. [Wells] The smallest palindromic composite such that some permutation of digits is prime. 121 is the only odd palindromic square with an odd number of digits that is divisible by a palindromic prime number with an even number of digits. [Luhn] Smallest palindrome pseudoprime to base 3. [De Geest] A palindrome whose prime factors are palindromic. [Russo] 121 can be expressed as the sum of a prime and its reversal for exactly three distinct primes. [Patterson] The smallest three-digit number such that the sum of the values that result by placing the exponentation symbol (^) between any two consecutive digits is prime. (I.e., 1^21+12^1 is prime.) [Opao]
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