There is none because the Least Common Denominator (or LCD) is the Least Common Multiple (LCM) of the denominators of two or more fractions.
You need at least two fractions to determine a least common denominator.
34
The LCD for 17 and 12 is 204
204
The only Least Common Multiple (LCM) for 17 16 is 272.
Their product.
A common denominator, though not the least, is 1700.
You need at least two fractions to determine a least common denominator.
68
It is 85
119
136
34
The LCD for 17 and 12 is 204
204
A single number cannot have anything in common. To find a lowest common denominator, you need to be adding or subtracting at least two fractions.
LCD(17, 19) = 323