All numbers can be broken down into factor pairs. No matter how many pairs there are, it's an even number of factors. Squares have a factor pair that consists of the same number twice. When you list them, you list the number once.
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All nonzero numbers have factors. Some factors are even numbers, some factors are odd numbers.
All but the square numbers - 53 of them.
Square numbers have an odd number of factors.
At least one of the factors of an even number must be even, because the product of odd factors is always odd.
All even numbers have at least one even prime factor.