The Natural Number 21

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Properties of the Number 21

  • Because 21 is not divisible by 2 ...
    • 21 is an odd number
    • 21 has parity 1
    • 21 is not an even number
  • Because 21 can be factored as 3 x 7 ...
    • 21 is a composite number
    • 21 is not a prime number

Alternative Representations of the Number 21

  • Base 2 (binary): 10101
  • Base 8 (octal): 25
  • Base 16 (hexadecimal): 15
  • Roman numeral: XXI
  • Words: twenty-one

Divisors of the Number 21

  • 21 has 4 positive divisors: 1, 3, 7, 21
    • The sum of the positive divisors is 32
  • 21 has 3 proper divisors: 1, 3, 7
    • The sum of the proper divisors is 11
  • 21 is a deficient number since the sum of the proper divisors is less than 21
  • 21 is not a perfect number
  • 21 is not an abundant number

More Properties of the Number 21

  • 21 is not a square number
  • 21 is not a cube number
  • 21 is not a palindromic number
  • 21 is a Fibonacci number
  • 21 is not a Lucas number

5:35 pm, Saturday, March 25, 2017 (UTC; +0000)
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