Backwards Read Primes

object Solution {
  def ifPrime(a: Long): Boolean ={
    if((a==2) | a==3) return true
    else  if(a%2==0) return false
    var b=3
    while (b<=a/b){
      if(a%b==0) return false
      else b+=2
    }
    return true
  }
  def rev(a: Long): Long ={
    var b = a.toString()
    b=b.reverse
    val a2=b.toLong
    a2
  }
  def backwardsPrime(start: Long, nd: Long): String = {
    var s = (start to nd).map(x => if(ifPrime(x) & ifPrime(rev(x)) & (x>10) & (x!=rev(x))) (x.toString + ",") else "").mkString("")
    if(s.length>1) s.substring(0,s.length-1) else s
  }
}