How is 89 a prime number

Hello,

10*10=100>89

n=89 is prime if it not divisible by all prime less then its square root

0<890<√89<10

The primes to test are 2,3,5,7.

89 does not end with a even digit = = > 89 is not divisible by 2

8+9=17 if not divisible by 3 = = >89 is not divisible by 3

89 does not end with 0 or 5 = = >89 is not divisible by 5

3*8+1*9=33 is not divisible by 7 = = >89 is not divisible by 7

So: 89 is prime.