Even numbers.
1
27 and 81 are a possibility. Also numbers like 5 and 10, 20 and 40.
Those numbers are called factors. A pair of those is called a factor pair.
2 and any even number.
That happens when one of the numbers is a factor of the other.
Numbers with more than one factor pair are composite numbers.
There is no Greatest Common Factor (GCF) for a single number. The Greatest Common Factor (GCF) is the largest factor common to two or more given numbers.
A prime number
One is.
Any pair of prime numbers
Even numbers.
A single number does not have a common factor. Common factors are factors that two or more numbers have in common. The greatest common factor of a pair of numbers over 50 could be any number, depending on the pair of numbers. The greatest common factor of 51 and 100 is 1. The greatest common factor of 51, 52, 53, 54, 55, and 56 is 1. The greatest common factor of 52 and 100 is 2. The greatest common factor of 57 and 102 is 3.
The least common factor of any set of numbers is 1.
1
yes
Yes, a pair of numbers can have fewer than two common factors. This only happens when the numbers are co-prime -- that is, when the numbers have only one common factor. In that case, the common factor is always 1.