Question

Which of the following numbers has the largest number of unique prime factors?: {85, 138, 317, 207}

Answer 1

`138` has the largest number of unique prime factors.

Explanation:

Prime factors of `85` are `5` and `17` as `85=5xx17`

Prime factors of `138` are `2`, `3` and `23` as `138=2xx3xx23`

`317` is itself prime as it does not have any factor other than `1` and itself.

Prime factors of `207` are `3` and `23` as `207=3xx3xx23`

Hence, `138` has the largest number of unique prime factors.