Q: Is 21,509 a Prime Number?
A: No, 21,509 is not a prime number.
A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 21509 can be evenly divided by 1 137 157 and 21,509, with no remainder.
Since 21,509 cannot be divided by just 1 and 21,509, it is not a prime number.