def is_sequence(nums):
    """Return True if a set of numbers is sequential i.e. 8, 11, 14, 17."""
    nums = sorted(list(nums))
    if len(nums) < 3:
        return False

    while nums:
        first_difference = nums[1] - nums[0]
        second_difference = nums[2] - nums[1]
        if first_difference != second_difference:
            return False

        if len(nums) < 4:
            break
        nums.pop(0)
    return True