text: function rBinarySearch(arr, num) {
      var holder = Math.floor(arr.length / 2);
      if (arr[holder] == num) {
          return true;
      } else if (num < arr[holder] && arr.length > 1) {
          return rBinarySearch(arr.slice(0, holder), num);
      } else if (num > arr[holder] && arr.length > 1) {
          return rBinarySearch(arr.slice(holder, arr.length), num);
      } else {
          return false
      }
  }
  // console.log(rBinarySearch([1, 2, 3], 1));
  
  function rGCF(x, y) {
      // this is the method of finding gcd
      if (x == y) {
          return x;
      }
      if (x > y) {
          return rGCF(x - y, y);
      }
      if (x < y) {
          return rGCF(x, y - x);
      }
  }
  
  // console.log(rGCF(7, 13));
  // console.log(rGCF(32, 48));
  
  function GCF(x, y) {
      if (x == y) {
          return x;
      }
      if (x > y) {
          if ((x / y) % 1 === 0) {
              return y;
          } else {
              return GCF(x - y, y);
          }
      }
      if (x < y) {
          if ((x / y) % 1 === 0) {
              return y;
          } else {
              return GCF(x, y -
                  x);
          }
      }
  }
  console.log(GCF(123456, 987654));