1800 is the greatest common factor of 1800 and 3600.
7 and 14
479 and 958 are two numbers whose greatest common factor is 479, among others.
All numbers have a common factor, even if it's only 1. Numbers whose greatest common factor is 1 are said to be relatively prime or co-prime.
29 and 4147
this is hard
8 and 16.
90 and 180
10 and 15
12 and 24.
8M and 12M2
4 and 9
12 and 20