There are not always an even number of factor pairs of a number - for example, prime numbers have an even number of factors, because they are divisible by themselves and 1, but this is only one pair of factors. However, for any square number, (for example, 3 x 3 = 9, 4 x 4 = 16), at least one of these factor pairs will consist of the same number repeated twice.
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These are the 16 factor pairs for the number 1,080:1080,1540,2360,3270,4216,5180,6135,8120,9108,1090,1272,1560,1854,2045,2440,2736,30
The factor pairs of 21 are:1, 213, 7Therefore, the number 21 has two pairs of positive integer factors.
All of the composite numbers less than 100 have factor pairs.
One divides any number
As I understand it, the number of factor pairs is equal to the number of rectangles.