The least common multiple (LCM) refers to a multiple that is COMMON to two or more numbers. You have only one number in the question! The least multiple of a number is itself.
The lcm, or lowest common multiple of 21 and 17 is 357.
The LCM is: 357
The LCM of 3, 5 and 7 is 105.
The LCM is: 357
357
357
357
357
The LCM of a single number is itself. To find the LCM requires two or more numbers.
The LCM of one number is itself, because LCM stands for least common multiple, it usually (in fact almost always) deals with two or more numbers.
The LCM is: 357
The Least Common Multiple (LCM) for 51 21 is 357.