almost_prime_numbers.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 14 February 2021
# https://github.com/trizen

# Generate k-almost prime numbers <= n. (not in sorted order)

# See also:
#   https://en.wikipedia.org/wiki/Almost_prime

func almost_prime_numbers(n, k, callback) {

    if (k == 1) {
        return n.each_prime(callback)
    }

    func (m, lo, k) {

        if (k == 1) {

            each_prime(lo, idiv(n, m), {|q|
                callback(m*q)
            })

            return nil
        }

        var hi = idiv(n,m).iroot(k)

        each_prime(lo, hi, {|q|
            __FUNC__(m*q, q, k-1)
        })
    }(1, 2, k)

    return callback
}

var n = 100
var k = 4

say gather {
    almost_prime_numbers(n, k, { take(_) })
}

__END__
[16, 24, 40, 56, 88, 36, 60, 84, 100, 54, 90, 81]