def binarySearch(numList, left, right, target):

    """
    Binary search for the range of number found in the exponential search algorithm
    :param left: the first number in the range of number
    :param right: the last number in the range of number
    :param numList: a list of number sorted in ascending order
    :param target: a number to be searched in the list of number
    :return: index of target or None if target is not found
    """

    if left > right:
        return -1
    mid = (left + right) // 2
    if target == numList[mid]:
        return mid
    elif target < numList[mid]:
        return binarySearch(numList, left, mid - 1, target)
    else:
        return binarySearch(numList, mid + 1, right, target)