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 |
Reading 991 in NumGrid context
For 991, the underlying data on this page comes from classical number theory plus NumGrid solver-derived puzzle statistics. The breakdown above is the federal record; the paragraphs below add the per-entity context that makes the headline numbers usable for a real decision rather than just a data lookup.
Every number on this page links back to classical number theory plus NumGrid solver-derived puzzle statistics; the methodology page describes the inputs, refresh cadence, and known limitations of the underlying data product.
For readers using this page as a decision input, the related-entity pages elsewhere on the site provide the comparison set. The most useful comparison for 991 is typically a peer within positive integers within the NumGrid target pool with similar size, similar exposure, or similar geography — not the national-level summary alone.
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.