A Prime number cannot be evenly divided by any number except itself and 1.
These are the prime numbers from 1 to 100:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 61, 71, 73, 79, 83, 89, 97
These are the composite numbers from 1 to 100:
4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99 and 100
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The factors of 100 are 1, 2, 4, 5, 10, 20, 25, 50, 100 2 and 5 are prime. 1 is neither. The rest are composite.
So we eliminate prime numbers. Note that the number 1 is neither prime nor composite. We have left:4689101214151618202122242526272830323334353638394042444546484950515254555657586062636465666869707274757677788081828485868788909192939495969899100
It is: 25*75 = 1875
The prime factors of 100 are 2, and 5. The composite factors are 100, 50, 25, 20, 10, and 4. A prime number has only 2 factors which are 1 and itself. Composite numbers are everything else except 1 and 0. 1 and 0 have a different name.
Composite numbers have more than two factors. So, the numbers which have two or less than two factors are not composite numbers. Numbers which have exactly two factors are prime numbers. 1 is an exceptional case because it is neither prime nor composite since it has only one factor which is 1.