func is_arithmetic(n) {
    n.tau `divides` n.sigma
}

say "The first one hundred arithmetic numbers:"
100.by(is_arithmetic).each_slice(10, {|*a|
    a.map { '%3s' % _ }.join(' ').say
})

for x in (1e3, 1e4, 1e5, 1e6) {
    var arr = x.by(is_arithmetic)
    say "\n#{x}th arithmetic number is #{arr.last}."
    say "There are #{arr.count{.is_composite}} composite arithmetic numbers <= #{arr.last}."
}