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The consecutive primes 1399 and 1409 have the property that
1399*1409 +/ (1399+1409) are both prime. Moreover,
7^13996^1399 is prime, and so is (12*10^139921)/99 =
1212...2121, a smoothly undulating palindromic prime with
1399 digits. [Hasler]
In 1882, Lucas noted that Le Lasseur found the first known prime factor (1399) of the Mersenne number 2^{233}1.
(There is one curio for this number that has not yet been approved by an editor.)
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