17

This number is a prime.

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From the sum of the first n primes one notices that from n = 2*17 to 2*21, all five end with the digit 7; the same as 17. The sums are 2127, 2427, 2747, 3087, 3447. [Bergot]

Subtract all the primes less than 17 from 17 and add the results if they are semiprimes. The result is the square of a prime. [Bergot]

Calculate the sum of the emirp 17 and its reversal. The sum of all prime factors of this number is 17. [Bergot]

(There are 11 curios for this number that have not yet been approved by an editor.)