You just divide it by 21 and if there is no remainder then it went in evenly.
3
Because 3 divides evenly into 21 and 36 with no remainder.
441 divides evenly by these numbers: 1 3 7 9 21 49 63 147 and 441.
A factor divides evenly into a given number.
Because 21 is the largest number that divides evenly into both of those numbers with no remainder.
A number that divides evenly into another number is called a factor.
1 is the smallest number that divides any positive integer evenly.
A factor divides evenly into a given number.
A number that divides into a whole number evenly is called a "factor" of that number.
Do the division, and see if there is a remainder.
The smallest prime number that divides 98 evenly is 2.