18

18 is an even composite number composed of two prime numbers multiplied together.

18 is an even composite number. It is composed of two distinct prime numbers multiplied together. It has a total of six divisors.

Prime factorization of 18:

2 × 32

(2 × 3 × 3)

See below for interesting mathematical facts about the number 18 from the Numbermatics database.

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Names Factors Divisors Scales Roots Fun

Names of 18

  • Cardinal: 18 can be written as Eighteen.

Scientific notation

  • Scientific notation: 1.8 × 101

Factors of 18

  • Number of distinct prime factors ω(n): 2
  • Total number of prime factors Ω(n): 3
  • Sum of prime factors: 5

Divisors of 18

  • Number of divisors d(n): 6
  • Complete list of divisors:
    1 2 3 6 9 18
  • Sum of all divisors σ(n): 39
  • Sum of proper divisors (its aliquot sum) s(n): 21
  • 18 is an abundant number, because the sum of its proper divisors (21) is greater than itself. Its abundance is 3

Bases of 18

  • Binary: 10010 2
  • Hexadecimal: 0x12

Squares and roots of 18

  • 18 squared (182) is 324
  • 18 cubed (183) is 5832
  • The square root of 18 is 4.2426406871
  • The cube root of 18 is 2.6207413943

Scales and comparisons

How big is 18?
  • To count from 1 to 18 would take you about nine seconds.

    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.

    Note: we do not count involuntary pauses, bathroom breaks or the necessity of sleep in our calculation!

  • A cube with a volume of 18 cubic inches would be around 0.2 feet tall.

Recreational maths with 18

  • 18 backwards is 81
  • 18 is a Harshad number.
  • The number of decimal digits it has is: 2
  • The sum of 18's digits is 9
  • More coming soon!

The information we have on file for 18 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!

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