primes.scala

#!/bin/bash

exec /opt/scala-2.10/bin/scala -feature "$0" "$@"
!#
object Primes {
  private lazy val notDivisibleBy2: Stream[Long] = 3L #:: notDivisibleBy2.map(_ + 2)
  private lazy val notDivisibleBy2Or3: Stream[Long] = notDivisibleBy2
      .grouped(3)
      .map(_.slice(1, 3))
      .flatten
      .toStream
  private lazy val notDivisibleBy2Or3Or5: Stream[Long] = notDivisibleBy2Or3
      .grouped(10)
      .map { g =>
        g.slice(1, 7) ++ g.slice(8, 10)
      }
      .flatten
      .toStream

  lazy val primes: Stream[Long] = 2L #::
      notDivisibleBy2.head #::
      notDivisibleBy2Or3.head #::
      notDivisibleBy2Or3Or5.filter { i =>
        i < 49 || primes.takeWhile(_ <= Math.sqrt(i).toLong).forall(i % _ != 0)
      }

  def <(n: Long): Stream[Long] = primes.takeWhile(_ <= n)
}

println((Primes < 1048576).last)