Is 87 a prime number?
87 is not a prime number. Here is a way to check it.
The answer
No. 87 is not a prime number: 3 × 29 = 87.
How to see that 87 is not prime
Its digits add up to 8 + 7 = 15, which is a multiple of 3. That means 87 is a multiple of 3 too, so 3 is a factor.
87 has four factors: 1 and 87, plus one pair in between, 3 and 29.
Split 87 into prime factors
87 splits straight into two primes, 3 × 29, so its factor tree has only one branch.
87 in the times tables
No fact from the 2 to 12 times tables, up to × 12, makes 87. Its smallest pair, 3 × 29, needs the 29 times table, which goes past 12.
Quick checks that catch 87
- The digits add up to 15, which is in the 3 times table, so 3 goes in.
87 at a glance
Optional extra number facts:
- In words
- eighty-seven
- In Roman numerals
- LXXXVII
- Odd or even
- Odd: it ends in 7
- Its factors add up to
- 120, or 33 without 87 itself. 87 is deficient: Deficient means this sum is less than the number.
The numbers either side of 87
- 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
- 88 is not prime. 88 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 88. Check 88 in full
Turn the digits round
87 backwards is 78. 78 is not prime. 78 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 78. Check 78 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 87?
83 below it and 89 above it, a gap of 6.
What is 87 squared?
87 × 87 = 7569.
What is the smallest number with as many factors as 87?
6. It has 4 factors, the same as 87.
Continue your number practice
Explore the diagnostic for another set of practice questions.