// Third Version of Ramanujan's Taxi
  def ramtaxi_O2(n: Long) = {
    val mapSums = mutable.HashMap.empty[Long, List[(Long, Long)]]
    var overOne = mutable.SortedSet[Long]()
    for (a <- 1L to n) {
      val a3 = a * a * a
      if (a3 <= n)
        for (b <- a to n) {
          val b3 = b * b * b
          if (b3 <= n) {
            val ab3 = a3 + b3
            mapSums += (ab3 -> ((a3, b3)
              :: mapSums.getOrElse(ab3, List())))
            if (mapSums(ab3).length > 1)
              overOne += ab3
          }
        }
    }
    overOne foreach {x => println(x + " = " + mapSums(x))}
  }
}