21 has only two factors , 3 and 7
Both are prime numbers, divisible only by itself and 1
So the third number must be .... 1
1 x 3 x 7 = 21
( Of course this only applies, if we are talking about integers ;-) )
Chat with our AI personalities
Any number can be multiplied by 21
Any number can be multiplied to get the answer 441. For example 5 can be multiplied by 88.2 If the question was which number can be multiplied by itself, the answers are: -21 and +21
3*7 = 21
21 and 5
21