20 (number) - in Mathematics

In Mathematics

  • 20 is a tetrahedral number as 20 = 1 + 3 + 6 + 10.
  • 20 is the basis for vigesimal number systems.
  • 20 is the third composite number comprising the product of a squared prime and a prime, and also the second member of the (22)q family in this form.
  • 20 has an aliquot sum of 22 (110% in abundance). Accordingly, 20 is the third abundant number and demonstrates an 8 member aliquot sequence; {20, 22, 14, 10, 8, 7, 1, 0}.
  • 20 is the smallest primitive abundant number.
  • 20 is the 4th composite number in the 7-aliquot tree. Two numbers have 20 as their aliquot sum; the discrete semiprime 34 and the squared prime 361. Only 2 other square primes are abundant 12 and 18.
  • An icosahedron has 20 faces. A dodecahedron has 20 vertices.
  • 20 can be written as the sum of three Fibonacci Numbers uniquely, i.e. 20 = 13 + 5 + 2.
  • The product of the number of divisors and the number of proper divisors of 20 is exactly 20.
  • 20 is the number of quarter or half turns required to optimally solve a Rubik's Cube in the worst case.
  • 20 is the only number with more than one digit that can be written from base 2 to base 20 using only the digits 0 to 9.

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