Eduardo thinks of a number between 1 and 20 that has exactly 5 factors. What number is he thinking of?
2 Answers
Answer is
Explanation:
It is apparent that a number cannot be a prime number, if it has exactly
As a product of two prime numbers say
Now for remaining
Hence answer is
Explanation:
The most direct method of finding the number that has
This is because factors are always in pairs, but in a square, one of the factors is multiplied by itself and it is only counted once. (the square root)
This means that of all the numbers from
It would seem that the largest one is most likely to have
Factors of
As a check, let's consider the other squares: