odd, prime · 991st positive integer
The number 991
991 is an odd prime number. It is the 991st positive integer.
Quick reference
| Prime factorization | 991 (prime) |
| Divisors | 1, 991 |
| Binary | 1111011111 |
| Hexadecimal | 0x3DF |
| Roman numeral | CMXCI |
| Digit sum | 19 |
| Properties | odd, prime |
Frequently asked
Is 991 a prime number?
Yes. 991 is prime — its only divisors are 1 and itself.
What are the factors of 991?
The factors (divisors) of 991 are 1, 991.
What is 991 in binary?
991 in binary is 1111011111. In hexadecimal it's 3DF.
What is 991 as a Roman numeral?
991 in Roman numerals is CMXCI.
What's the digit sum of 991?
Adding the digits of 991: 9 + 9 + 1 = 19.