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Old 2009-09-28, 16:40   #6
fivemack
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Feb 2006
Cambridge, England

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You give it the starting point, and you give it a list of primes which divide some numbers in the sequence after that starting point; it refactorises everything, it's just that the first method it uses is trial division by a set of primes known to include the factors, which is really quick.

And then having done the factorisation it computes sigma(n)-n and continues.
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