Question

Is the number 87 prime, composite, or neither?

Answer 1

I wonder what you mean by 'neither'. But 87 is composite.

Explanation:

Try dividing by primes from 2 up and see if something is left (we call that the mode, and it's zero when divisable):

`87//2=43`, with 1 left
`87//3=29`, none left, so `87=3xx29`

Now we try `29`. We don't have to try `2` anymore:

`29//3=14` with 2 left
`29//5=5`, with 4 left

We don't have to try `7` or above, because if
`29=7xx"something"`, that something would be smaller than `7` and already been found.
So `29` is a prime, and the complete factorization into primes:

`87=3xx29`