val from2 = Stream.iterate(2: BigInt)(_+1)

def sieve(xs: Stream[BigInt]): Stream[BigInt] = {
  val x = xs.head
  xs.tail.filter((y: BigInt) => y % x != 0)
}

val primes = {
  val seqs = Stream.iterate(from2)(sieve)
  seqs.map(_.head)
}

// try
// primes.take(100).toList