Is 75 a prime number?
75 is not a prime number. Here is a way to check it.
The answer
No. 75 is not a prime number: 3 × 25 = 75.
How to see that 75 is not prime
Its digits add up to 7 + 5 = 12, which is a multiple of 3. That means 75 is a multiple of 3 too, so 3 is a factor.
75 has 6 factors (1, 3, 5, 15, 25 and 75), which make 3 factor pairs.
Split 75 into prime factors
Split off the smallest prime each time, and keep going until every part is prime:
- 75 = 3 × 25
- 75 = 3 × 5 × 5
With repeated primes written as powers, that is 3 × 5². A small raised number tells you how many times to use that factor: for example, 2³ means 2 × 2 × 2.
75 in the times tables
No fact from the 2 to 12 times tables, up to × 12, makes 75. Its smallest pair, 3 × 25, needs the 25 times table, which goes past 12.
See the 25 times table, where 25 × 3 = 75 is one of the facts.
Quick checks that catch 75
- The digits add up to 12, which is in the 3 times table, so 3 goes in.
- It ends in 5, so 5 goes in.
75 at a glance
Optional extra number facts:
- In words
- seventy-five
- In Roman numerals
- LXXV
- Odd or even
- Odd: it ends in 5
- Its factors add up to
- 124, or 49 without 75 itself. 75 is deficient: Deficient means this sum is less than the number.
The numbers either side of 75
- 74 is not prime. 74 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 74. Check 74 in full
- 76 is not prime. 76 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 76. Check 76 in full
Turn the digits round
75 backwards is 57. 57 is not prime. Its digits add up to 5 + 7 = 12, which is a multiple of 3. That means 57 is a multiple of 3 too, so 3 is a factor. Check 57 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 75?
73 below it and 79 above it, a gap of 6.
What is 75 squared?
75 × 75 = 5625.
What is the smallest number with as many factors as 75?
12. It has 6 factors, the same as 75.
Continue your number practice
Explore the diagnostic for another set of practice questions.