Sieve of

sieve.scala

def sieve(maxNumber: Int) = {
  def innerSieve(p: Int, n: Int, a: Array[Boolean]): Array[Boolean] = 
    if (p >= a.size) a
    else if (!a(p) || n >= a.size) innerSieve(p+1, 2*(p+1), a)
    else { a(n) = false ; innerSieve(p, p + n, a) }
  innerSieve(2, 2, Array.fill(maxNumber+1)(true)).zipWithIndex.filter(_._1).map(_._2)
}