fun main() {
    val primes = sequence {
        var nums = generateSequence(2) { x -> x + 1 }
        while (true) {
            val a = nums.elementAt(0)
            yield(a)
            nums = nums.drop(1).filter { b -> b % a != 0 }
        }
    }
    println(primes.take(20).toList())
}