Q&A for How to Check if a Number Is Prime

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Why do I use odd numbers in testing for primes?

Community Answer

Because, other than 2, there can be no even prime numbers (they would be divisible by 2).

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Are 57, 87, 89, and 91 prime numbers?

Gaurav Wasnik

Community Answer

57 is divisible by 3 and 19 in addition to 1 and itself so it is not prime. 87 is also divisible by 3 so it is not prime. 89 is a prime number because it is only divisible by 1 and itself. 91 is divisible by 7 so it is not prime.

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Is it true that since 43 x 1069 = 45,967, it can't be a prime number?

Community Answer

Yes. Prime numbers cannot be the product of any two numbers other than 1 and the number itself. So 45,967 is not prime.

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Do prime numbers have a pattern?

Community Answer

Unfortunately, there isn't any obvious or useful patterns among prime numbers.

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Are there any at-a-glance quick way to have a good guess at whether a number is prime or not?

Donagan

Top Answerer

No, not at a glance. The closest you can come is knowing that a prime number is always odd but never ends in a 5. A prime number will end in a 1, 3, 7, or 9, but not all such numbers are prime.

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Is it true that since 43 x 1069 = 45,967, it can't be a prime number?

I_l1ke_gam3s

Community Answer

Yes. A prime number has factors of only 1 and itself.

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