Question: Check if an integer is part of the factorisation of another number


I am working on a Dirichlet breakdown of primes. I need a way to check if a number is part of anothers number factorization.

Example: 30 = 2*3*5.

2 is therefore part of the ifactor of 30. 4 and 7 are not.
How do I check if, for instance, 7 is part of de factorization of 390?

Thanks in advance.

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