Is 51 a prime number ... People think it's prime
Well, those people are wrong. You can factor 51 to (3 • 17)
To see if that is prime or not, you could check its divisibility rules.
If it is divisible by 2, then it is an even number---51 is odd.
If it is divisible by 3, then the digits sum to a number divisible by 3, 5 + 1 = 6, and 6 is divisible by 3.
Thus, 51 is divisible by 3.
Remember the divisibility rules Guest!