Is 25 a prime number?
25 is not a prime number. Here is a way to check it.
The answer
No. 25 is not a prime number: 5 × 5 = 25.
How to see that 25 is not prime
25 ends in 5, and every number ending in 5 or 0 is in the 5 times table, so 5 is a factor.
25 has only three factors, 1, 5 and 25: just one more than a prime has, which is still enough to rule it out.
Split 25 into prime factors
25 is 5 × 5: the same prime twice, so its factor tree stops after one split.
25 in the times tables
Just one of the 2 to 12 times tables has 25 in it: 5 × 5 = 25.
Quick checks that catch 25
- It ends in 5, so 5 goes in.
25 at a glance
Optional extra number facts:
- In words
- twenty-five
- In Roman numerals
- XXV
- Odd or even
- Odd: it ends in 5
- Square number
- 5 × 5 = 25
- Its factors add up to
- 31, or 6 without 25 itself. 25 is deficient: Deficient means this sum is less than the number.
The numbers either side of 25
- 24 is not prime. 24 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 24. Check 24 in full
- 26 is not prime. 26 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 26. Check 26 in full
Turn the digits round
25 backwards is 52. 52 is not prime. 52 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 52. Check 52 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 25?
23 below it and 29 above it, a gap of 6.
What is 25 squared?
25 × 25 = 625.
What is the smallest number with as many factors as 25?
4. It has 3 factors, the same as 25.
Continue your number practice
Explore the diagnostic for another set of practice questions.