Is 85 a prime number?
85 is not a prime number. Here is a way to check it.
The answer
No. 85 is not a prime number: 5 × 17 = 85.
How to see that 85 is not prime
85 ends in 5, and every number ending in 5 or 0 is in the 5 times table, so 5 is a factor.
85 has four factors: 1 and 85, plus one pair in between, 5 and 17.
Split 85 into prime factors
85 splits straight into two primes, 5 × 17, so its factor tree has only one branch.
85 in the times tables
No fact from the 2 to 12 times tables, up to × 12, makes 85. Its smallest pair, 5 × 17, needs the 17 times table, which goes past 12.
See the 17 times table, where 17 × 5 = 85 is one of the facts.
Quick checks that catch 85
- It ends in 5, so 5 goes in.
85 at a glance
Optional extra number facts:
- In words
- eighty-five
- In Roman numerals
- LXXXV
- Odd or even
- Odd: it ends in 5
- Its factors add up to
- 108, or 23 without 85 itself. 85 is deficient: Deficient means this sum is less than the number.
The numbers either side of 85
- 84 is not prime. 84 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 84. Check 84 in full
- 86 is not prime. 86 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 86. Check 86 in full
Turn the digits round
85 backwards is 58. 58 is not prime. 58 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 58. Check 58 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 85?
83 below it and 89 above it, a gap of 6.
What is 85 squared?
85 × 85 = 7225.
What is the smallest number with as many factors as 85?
6. It has 4 factors, the same as 85.
Continue your number practice
Explore the diagnostic for another set of practice questions.