def contains_3_consecutive(list_of_nums):
    """Return True if the list contains 3 consecutive numbers each increasing by 1."""
    for i in range(len(list_of_nums) - 2):
        if (list_of_nums[i+1] == list_of_nums[i] + 1 and
            list_of_nums[i+2] == list_of_nums[i] + 2):
            return True

    return False