Erdös-Selfridge categorization of primes: Difference between revisions
Erdös-Selfridge categorization of primes (view source)
Revision as of 09:04, 15 April 2022
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<lang ecmascript>import "./math" for Int
import "./fmt" for Fmt
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var limit = (1e6.log * 1e6 * 1.2).floor // should be more than enough
var primes = Int.primeSieve(limit)
var prevCats = {}
var cat // recursive
cat = Fn.new { |p|
if (prevCats.containsKey(p)) return prevCats[p]
var pf = Int.primeFactors(p+1)
if (pf.all { |f| f == 2 || f == 3 }) return 1
if (p > 2) {
for (i in pf.count-1..1) {
if (pf[i-1] == pf[i]) pf.removeAt(i)
}
}
for (c in 2..11) {
if (pf.all { |f| cat.call(f) < c })
prevCats[p] = c
return c
}
}
return 12
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