experimental-projects/oeis-research/Antti Karttunen/Numbers k such that derivative(sigma(k)) = k/search.sf

#!/usr/bin/ruby

# Numbers k such that A003415(sigma(k)) = k, where A003415 is the arithmetic derivative, and sigma is the sum of divisors of n.
# https://oeis.org/A342021

# Known terms:
#   5, 8, 41, 47057

var min = 1e8
var max = 1e9

for n in (5..100) {

    var count = n.squarefree_almost_prime_count(min, max) || break

    say "\nTesting: n = #{n} (count: #{count})\n"

    n.each_squarefree_almost_prime(min, max, {|p|

        var d = p.derivative

        p.inverse_sigma.each {|k|
            if (d == k) {
                print(k, ", ")
            }
        }
    })
}