func propdiv (n) {
    n.divisors.first(-1)
}

{|i| printf("%2d: %s\n", i, propdiv(i)) } << 1..10

var max = 0
var candidates = []

for i in (1..20_000) {
    var divs = propdiv(i).len
    if (divs > max) {
        candidates = []
        max = divs
    }
    candidates << i if (divs == max)
}

say "max = #{max}, candidates = #{candidates}"