Is 619 prime or composite

Answer 1

The number 619 is the 114th Prime number.

To check if a number is prime or not, you can repeatedly divide integers into the number and see if any divide evenly. Spreasheets make this easy to repeatedly divide.

You only need to check up to the square root of the number that you are checking. Any numbers, larger than the square root, would show up as quotients when dividing. This method can be used to find all of the factors of a number. In this case, the square root of 619 is 24.88, so we only need to check up to 24.

If you're doing this type of problem say on a test where you're dividing out by

hand, then it's best to memorize some prime numbers, so actually you only

have to divide by them:

So you can divide by 2,3,5,7,11,13,17,19,23.

There are many simple division tests for integers, some of which can be utilized for this type of problem. For example, a number is divisible by 2 if and only if it is even. A number is divisible by 3 if and only if the sum of its digits is a multiple of three (that process can be repeated multiple times until the result is easy to divide by 3). Divisibility by 5 can be tested by looking at the last digit. It must be a 5 or a 0. Other divisibility tests exist as well.