Take your pick out of: 23 29 31 37 41 43 and 47 because as prime numbers they have only two factors
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53
Just two: 1 and the number itself.
Both 5 and 7 are prime numbers. That means there are only two factors of each number, 1 and the number itself. There are no common factors between the two.
28
97 is the only prime number between 90 and 100.