53

 

If in doubt as to if a number is prime check it on that link I have in my opening post.

 

All odd numbers ending with 5 are divisble by 5 so, other than 5, they cannot be prime.
Any number where the sum of the individual digits is divisible by 3 is itself also divisible by 3 so won't be prime, other than 3, So for 45: 4+5=9 which is divisble by 3 so 45 is divisble by 3 for instance. That only works for 3 and doesn't work for any other number (other than 9).

Add Reply

Likes (0)
Post
×
×
×
×
×