Practical numbers: Difference between revisions
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(→Python: Faster version: Whoops) |
(→Python: Faster version: Check sum of factors can reach x-1.) |
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the sets. 720, another Practical number needs just 0.01% of its half a billion sets to prove it is Practical. |
the sets. 720, another Practical number needs just 0.01% of its half a billion sets to prove it is Practical. |
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The inner loop is sensitive to the order of factors passed to the powerset generator and experimentation shows that reverse sorting the factors saves the most computation. |
The inner loop is sensitive to the order of factors passed to the powerset generator and experimentation shows that reverse sorting the factors saves the most computation.<br> |
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An extra check on the sum of all factors has a minor positive effect too. |
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<lang python>def is_practical5(x: int) -> bool: |
<lang python>def is_practical5(x: int) -> bool: |
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f = sorted(factors5(x), reverse=True) |
f = sorted(factors5(x), reverse=True) |
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if sum(f) < x - 1: |
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return False # Never get x-1 |
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ps = powerset(f) |
ps = powerset(f) |
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