Quick tip to see if a number is prime

Wednesday, November 18, 2020

Which of these numbers are prime?


In this example 31 and 37 are prime.

A shortcut to see if a number is prime is to follow these rules.
Step 1. Find the square root of the number.
For example, the square root of 36 is 6.

Step 2. Find the prime factors of the square root.
For 6 = 2 and 3

Step 3. If the original number is divisible by these prime numbers then it is a composite number, if it is not divisible then it is prime.
36 is divisible by 2 and 3 so it is a composite number.

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