7 has two factors, one and itself. For them to be common, they need to be compared to another set of factors.
The Greatest Common Divisor (GCD) for 5 7 is 1
The common divisors are: 1, 2, 7, 14.
2 divisors: 1, 7
The GCF is 7.
Since 7 is a prime, its only divisors are 1 and 7.
1, 2, 7, and 14 are common divisors (and common factors) of 28 and 42.
The divisors of 35 are: 1, 5, 7, 35.
The divisors of 21 are: 1, 3, 7, 21.
231 has 8 divisors.
The divisors of 63 are: 1, 3, 7, 9, 21, 63.
The divisors of 147 are 1, 3, 7, 21, 49, 147.
All numbers have divisors. Some numbers have some of the same divisors as other numbers. These are called common divisors. 3 is a divisor of 9. 3 is a divisor of 12. 3 is a common divisor of 9 and 12.