# 991

## 991 is a prime number. Like all primes greater than two, it is odd and has no factors apart from itself and one.

What does the number 991 look like?

As a prime, it is not composed of any other numbers and has no internal structure.

991 is a prime number. Like all primes (except two), it is an odd number.

## Prime factorization of 991:

### 991

See below for interesting mathematical facts about the number 991 from the Numbermatics database.

### Names of 991

• Cardinal: 991 can be written as Nine hundred ninety-one.

### Scientific notation

• Scientific notation: 9.91 × 102

### Factors of 991

• Number of distinct prime factors ω(n): 1
• Total number of prime factors Ω(n): 1
• Sum of prime factors: 991

### Divisors of 991

• Number of divisors d(n): 2
• Complete list of divisors:
• Sum of all divisors σ(n): 992
• Sum of proper divisors (its aliquot sum) s(n): 1
• 991 is a deficient number, because the sum of its proper divisors (1) is less than itself. Its deficiency is 990

### Bases of 991

• Binary: 11110111112
• Base-36: RJ

### Squares and roots of 991

• 991 squared (9912) is 982081
• 991 cubed (9913) is 973242271
• The square root of 991 is 31.4801524773
• The cube root of 991 is 9.9699095473

### Scales and comparisons

How big is 991?
• 991 seconds is equal to 16 minutes, 31 seconds.
• To count from 1 to 991 would take you about eight minutes.

This is a very rough estimate, based on a speaking rate of half a second every third order of magnitude. If you speak quickly, you could probably say any randomly-chosen number between one and a thousand in around half a second. Very big numbers obviously take longer to say, so we add half a second for every extra x1000. (We do not count involuntary pauses, bathroom breaks or the necessity of sleep in our calculation!)

• A cube with a volume of 991 cubic inches would be around 0.8 feet tall.

### Recreational maths with 991

• 991 backwards is 199
• The number of decimal digits it has is: 3
• The sum of 991's digits is 19
• More coming soon!