21,991 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 21991 look like?

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

21991 is a prime number. Like all primes (except two), it is an odd number.

Prime factorization of 21991:


See below for interesting mathematical facts about the number 21991 from the Numbermatics database.

Names of 21991

  • Cardinal: 21991 can be written as Twenty-one thousand, nine hundred ninety-one.

Scientific notation

  • Scientific notation: 2.1991 × 104

Factors of 21991

  • Number of distinct prime factors ω(n): 1
  • Total number of prime factors Ω(n): 1
  • Sum of prime factors: 21991

Divisors of 21991

  • Number of divisors d(n): 2
  • Complete list of divisors:
  • Sum of all divisors σ(n): 21992
  • Sum of proper divisors (its aliquot sum) s(n): 1
  • 21991 is a deficient number, because the sum of its proper divisors (1) is less than itself. Its deficiency is 21990

Bases of 21991

  • Binary: 1010101111001112
  • Hexadecimal: 0x55E7
  • Base-36: GYV

Squares and roots of 21991

  • 21991 squared (219912) is 483604081
  • 21991 cubed (219913) is 10634937345271
  • The square root of 21991 is 148.2936276447
  • The cube root of 21991 is 28.0165718227

Scales and comparisons

How big is 21991?
  • 21,991 seconds is equal to 6 hours, 6 minutes, 31 seconds.
  • To count from 1 to 21,991 would take you about six hours.

    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 21991 cubic inches would be around 2.3 feet tall.

Recreational maths with 21991

  • 21991 backwards is 19912
  • The number of decimal digits it has is: 5
  • The sum of 21991's digits is 22
  • More coming soon!

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"Number 21991 - Facts about the integer". Numbermatics.com. 2022. Web. 30 June 2022.

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Numbermatics. (2022). Number 21991 - Facts about the integer. Retrieved 30 June 2022, from https://numbermatics.com/n/21991/

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Numbermatics. 2022. "Number 21991 - Facts about the integer". https://numbermatics.com/n/21991/

The information we have on file for 21991 includes mathematical data and numerical statistics calculated using standard algorithms and methods. We are adding more all the time. If there are any features you would like to see, please contact us. Information provided for educational use, intellectual curiosity and fun!

Keywords: Divisors of 21991, math, Factors of 21991, curriculum, school, college, exams, university, Prime factorization of 21991, STEM, science, technology, engineering, physics, economics, calculator, twenty-one thousand, nine hundred ninety-one.

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