Scalaで２数値間の素数の個数検出

PrimeNumCounter.scala

import scala.math.sqrt
import scala.collection.mutable.ArrayBuffer

object PrimeNumCounter {
  def main(args:Array[String]) {
    println(countPrimeNum(args(0).toInt, args(1).toInt))
  }

  def countPrimeNum(start:Int, end:Int) = {
    var primeList:ArrayBuffer[Int] = ArrayBuffer[Int](2)
    var numList:List[Int] = (3 to end by 2).toList

    while(numList.head < sqrt(end)) {
      primeList += numList.head
      numList = numList.filterNot( e => e%primeList.last == 0 )
    }
    primeList.count(n=> n >= start) + numList.count(n=> n >= start)
  }
}