Q: Is 21,978 a Prime Number?
A: No, 21,978 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 21978 can be evenly divided by 1 2 3 6 9 11 18 22 27 33 37 54 66 74 99 111 198 222 297 333 407 594 666 814 999 1,221 1,998 2,442 3,663 7,326 10,989 and 21,978, with no remainder.
Since 21,978 cannot be divided by just 1 and 21,978, it is not a prime number.