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Prime numbers, except 2, are always odd (they would not be prime if they were even cos they would be divisible by 2.) 1 less than any odd number must be an even number.
No square number is a prime number, since it has the number you squared as a factor. There are several square numbers less than 100. Just calculate the squares of all numbers, starting with 1, until you reach or pass 100. Then stop.
3 is prime, 1 less than the perfect square of 4 (2x2)
87 is the only 2-digit number that is 6 greater and 13 less than a square, but it is not prime.
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