Sieve of Eratosthenes in scala

Eratosphen.scala

import scala.annotation.tailrec
import java.nio.file.{Paths, Files}
import java.nio.charset.StandardCharsets

type Longs = List[Long]

/* Eratosphen */
def eratosphen(targetNumber: Long): Longs = {
  require(targetNumber > 2)

  @inline def isPrime(current: Long, divisors: Longs) =
    !divisors.exists(current % _ == 0)

  @tailrec def rec(current: Long, divisors: Longs, output: Longs): Longs =
    if (current == targetNumber)
      output
    else if (isPrime(current, divisors))
           rec(current + 1, current::divisors, current::output)
         else
           rec(current + 1, divisors, output)

  rec(2, Nil, Nil)
}


/* Setup, IO*/
val target = 1000000
val timerStart = System.nanoTime
val result = eratosphen(target)
val timerStop = System.nanoTime

val resultString =
  result.mkString(s"Prime numbers, time spent ${timerStop - timerStart}: \n",",\n", "\n")

Files.write(
  Paths.get("output.txt"),
  resultString.getBytes(StandardCharsets.UTF_8))