Q: Is 21,605 a Prime Number?
A: No, 21,605 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 21605 can be evenly divided by 1 5 29 145 149 745 4,321 and 21,605, with no remainder.
Since 21,605 cannot be divided by just 1 and 21,605, it is not a prime number.