Is 40 a prime number?
40 is not a prime number. Here is a way to check it.
The answer
No. 40 is not a prime number: 2 × 20 = 40.
How to see that 40 is not prime
40 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 40.
40 has 8 factors (1, 2, 4, 5, 8, 10, 20 and 40), which make 4 factor pairs.
Split 40 into prime factors
Split off the smallest prime each time, and keep going until every part is prime:
- 40 = 2 × 20
- 40 = 2 × 2 × 10
- 40 = 2 × 2 × 2 × 5
With repeated primes written as powers, that is 2³ × 5. A small raised number tells you how many times to use that factor: for example, 2³ means 2 × 2 × 2.
40 in the times tables
40 turns up in 4 different times tables, the 4, 5, 8 and 10: 4 × 10, 5 × 8, 8 × 5 and 10 × 4.
Quick checks that catch 40
- The last digit, 0, is even, so 2 goes in.
- Half of it is 20, which is still even, so 4 goes in.
- It ends in 0, so 5 goes in.
- It ends in 0, so 10 goes in.
40 at a glance
Optional extra number facts:
- In words
- forty
- In Roman numerals
- XL
- Odd or even
- Even: it ends in 0
- Multiple of 10
- 4 tens
- Its factors add up to
- 90, or 50 without 40 itself. 40 is abundant: Abundant means this sum is greater than the number.
The numbers either side of 40
- 39 is not prime. Its digits add up to 3 + 9 = 12, which is a multiple of 3. That means 39 is a multiple of 3 too, so 3 is a factor. Check 39 in full
- 41 is prime: 2, 3 and 5 do not go into it, and 7 × 7 is already past 41. Check 41 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 40?
37 below it and 41 above it, a gap of 4.
What is 40 squared?
40 × 40 = 1600.
What is the smallest number with as many factors as 40?
24. It has 8 factors, the same as 40.
Continue your number practice
Explore the diagnostic for another set of practice questions.