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Old 2019-03-24, 13:13   #2
CRGreathouse
 
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Aug 2006

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I can improve your test. This works without assuming Lehmer's conjecture:

Let x be a positive integer.

If f(x) = x-1 return PRIME
If f(x) < x-1 return COMPOSITE
If f(x) > x-1 return UNIT

Now all you have to do is find a way to compute f(x) quickly and you're done!
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