experimental-projects/oeis-research/Ilya Gutkovskiy/Number of subsets of {1..n} whose harmonic mean is an integer/prog.sf

#!/usr/bin/ruby

# Number of subsets of {1..n} whose harmonic mean is an integer.
# https://oeis.org/A339453

func a(n) is cached {

    if (n.is_prime_power) {   # a(p^k) = a(p^k-1)+1
        var p = n.perfect_root
        var k = n.perfect_power
        return (a(p**k - 1)+1)
    }

    var count = 0

    @(1..n) -> subsets {|*a|
        if (Math.harmonic_mean(a...).is_int) {
            ++count
        }
    }

    return count
}

for k in (1..100) {
    print(a(k), ", ")
}