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56 (another Prime Pages' Curiosity) |
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Sigma(56) equals the first prime of the form 6n - 1 factorial, 5!. [Noll] 256 - 1 - 56 + 1 is prime. [Noll] The number of products of distinct primes less than or equal to 11 (the only palindromic prime with an even number of digits) which are congruent to -1 mod 11 is 56. [Noll] D. H. Lehmer showed that Meissel's calculation of primes less than a billion was 56 too few. 56 letters are required to write the famous prime number 6700417 in English. The product of all composite numbers up to 56 (i.e. Compositorial 56) plus 1 is prime. Note that this prime consist of 56 digits. [Gupta]
56 = sigma(sigma(sigma(5+6 ))) and 5+6 = The smallest number that can be expressed as a sum of two primes, each ending with the digit 3, in two different ways (56 = 3 + 53 = 13 + 43). [Sladcik]
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