Factors of 85
The factors of 85 are 1, 5, 17, 85. No, 85 is a composite number. Its prime factorization is 5 × 17.
Factor pairs of 85
Every factor has a partner that multiplies with it to give 85. Listing pairs from the outside in is the fastest way to find all the factors: once the two numbers in a pair meet in the middle, you have them all.
| Pair | Check |
|---|---|
| 1 and 85 | 1 × 85 = 85 |
| 5 and 17 | 5 × 17 = 85 |
Prime factorization of 85, step by step
Divide by the smallest prime that goes in evenly, then repeat on the result until you reach 1. The divisors you used are the prime factors.
| Step | Divide | Result |
|---|---|---|
| 1 | 85 ÷ 5 | 17 |
| 2 | 17 ÷ 17 | 1 |
So 85 = 5 × 17, written compactly as 5 × 17.
Divisibility checks for 85
The quick rules a student uses before dividing, applied to 85:
| Divisible by | Rule | For 85 | Result |
|---|---|---|---|
| 2 | last digit is even | last digit 5 | no |
| 3 | digit sum divisible by 3 | digits add to 13 | no |
| 4 | last two digits divisible by 4 | 85 ÷ 4 | no |
| 5 | last digit is 0 or 5 | last digit 5 | yes |
| 6 | divisible by both 2 and 3 | odd, digit sum 13 | no |
| 8 | last three digits divisible by 8 | 85 ÷ 8 | no |
| 9 | digit sum divisible by 9 | digits add to 13 | no |
| 10 | last digit is 0 | last digit 5 | no |
Frequently Asked Questions
What are the factors of 85?
The factors of 85 are 1, 5, 17, 85.
Is 85 a prime number?
No, 85 is a composite number. Its prime factorization is 5 × 17.
How many factors does 85 have?
85 has 4 factors. You can get that count from the prime factorization without listing them: add 1 to each exponent in 5 × 17 and multiply -- (1+1) × (1+1) = 4.
Is 85 even or odd?
85 is odd (2 is not a factor).
What is the sum of the factors of 85?
1 + 5 + 17 + 85 = 108. Leaving out 85 itself, the proper factors add to 23, less than 85, so 85 is a deficient number.
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