Number 18 . In mathematics, particularly in arithmetic , the number 18 is a natural number that follows 17 and precedes 19. Eighteen is written and read in Spanish , in addition to Indian-Arabic notation; its representation in Roman numerals is XVIII .
Summary
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- 1 Arithmetic properties
- 2 Severability
- 3 Numerical diversity
- 4 Geometry
- 5 Source
Arithmetic properties
- is twice a square: 9,
- is twice an odd number
- is the average of two twin rational cousins: 17 and 19
- in the set of natural numbers is a composite number
- in the set of even numbers, 0, ± 2, ± 4, ± 6, …, 18 does not have a divisor, since there is no pair that divides it and the quotient is even.
Divisibility
- as a natural number it has 6 divisors; 1,2,3,6,9,18
- are proper divisors 2,3,6,9
- As an integer it has 12 divisors: ± 1, ± 2, ± 3, ± 6, ± 9, ± 18
- Euler’s function for 18: 6;
- the respective coprimes are: 1,5,7,11,13, 17
- A number N, necessarily even, is divisible by 18, if the sum of all digits is 0 or a multiple of 9.Exm. 28 188.
Numerical diversity
- is an integer 18 = {(18.0), (19.1), (20.2), (21.43, …}
- is a rational number 18 = {(18.1), (36.2), (54.3), (72.4), …}
- is real number: 18 = 17,9999 …
- it is a complex number, a binomial form; 18 + 0i
- is algebraic number, solution of the equation 3t -54 = 0
Geometry
- A simple 18-sided polygon is called an octodecagon
- There are 18-sided prisms at the bases are hexagonal and the sides are rectangular (or rhomboid)
- There is a pyramid with 17 triangular faces and the base is a heptadecagon.
