Is 66 a prime number?
66 is not a prime number. Here is a way to check it.
The answer
No. 66 is not a prime number: 2 × 33 = 66.
How to see that 66 is not prime
66 is even, and every even number can be divided by 2, so 2 is a factor as well as 1 and 66.
66 has 8 factors (1, 2, 3, 6, 11, 22, 33 and 66), which make 4 factor pairs.
Split 66 into prime factors
Split off the smallest prime each time, and keep going until every part is prime:
- 66 = 2 × 33
- 66 = 2 × 3 × 11
66 in the times tables
66 turns up in 2 different times tables, the 6 and 11: 6 × 11 and 11 × 6.
Quick checks that catch 66
- The last digit, 6, is even, so 2 goes in.
- The digits add up to 12, which is in the 3 times table, so 3 goes in.
- It is even and passes the check for 3 as well, so 6 goes in.
- Its two digits match, and every two-digit number like that is in the 11 times table.
66 at a glance
Optional extra number facts:
- In words
- sixty-six
- In Roman numerals
- LXVI
- Odd or even
- Even: it ends in 6
- Triangular number
- 1 + 2 + … + 11 = 66, a triangle of counters with 11 on the bottom row
- Its factors add up to
- 144, or 78 without 66 itself. 66 is abundant: Abundant means this sum is greater than the number.
The numbers either side of 66
- 65 is not prime. 65 ends in 5, and every number ending in 5 or 0 is in the 5 times table, so 5 is a factor. Check 65 in full
- 67 is prime: 2, 3, 5 and 7 do not go into it, and 11 × 11 is already past 67. Check 67 in full
Related pages
More numbers
Questions parents ask
Which prime numbers are either side of 66?
61 below it and 67 above it, a gap of 6.
What is 66 squared?
66 × 66 = 4356.
What is the smallest number with as many factors as 66?
24. It has 8 factors, the same as 66.
Continue your number practice
Explore the diagnostic for another set of practice questions.