The book is now available! 521
(another Prime Pages' Curiosity)
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If p is prime, then it divides the pth term of the Perrin sequence: 0, 2, 3, 2, 5, 5, 7, 10, 12, 17, ... (each term is the sum of the two terms preceding the term before it). Often, if n > 1 divides the nth term, then n is prime. The first of infinitely many exceptions to this rule is the square of 521. There are only 17 such composites less than 10^9.

 

  Submitted: 2008-04-10 15:40:57;   Last Modified: 2009-02-20 21:38:13.



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