Erdös-Selfridge categorization of primes: Difference between revisions
Erdös-Selfridge categorization of primes (view source)
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1+>./0,pcat(q:1+y)-.2 3
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Explanation: this is a recursive function defined only on primes. We memoize it for good performance.
To find the prime category of a prime, we find the prime factorization of the next larger integer, and find the category of each of those factors other than 2 or 3. The category 1 one greater than the maximum of these categories (with an explicit 0 for the maximum when there are no such factors)
First 200 primes -- category is in left box, primes are in right box:
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