﻿ Number — Math18

Math18

# Number

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## The Meaning of Numbers

The term number comes from the Latin "numĕrus" and refers to the expression of a quantity in relation to its unit, therefore, it is an expression of the relation between quantity and unit. The science focused on the study of numbers that corresponds to their properties and the operations that can be performed with them is arithmetic, which is a main branch of mathematics.

Knowing how to understand numbers helps us in our lives and that is why there is a science known as numerology, which is responsible for studying the meaning of numbers and their relationship with everything around us.

## Classification of the numbers

The numbers are classified into five main types:

• Natural numbers: They are represented with an "N", corresponds to any number that is greater than zero (0), in other words any positive number. It is important to consider that natural numbers cannot have a decimal, fractional, or imaginary part. N = [1, 2, 3, 4,…, + infinity)

Note: Some authors include zero as a natural number.

• Integer numbers: They are represented with a "Z", corresponds to any natural number, to zero and negative numbers are included. Since they must be integers, they cannot have a decimal, fractional, or imaginary part. Z = (- infinity,…, -2, -1, 0, 1, 2,…, + infinity)
• Rational numbers: They are represented with a "Q", they are those whose numbers can be expressed as a fraction of two whole numbers. Q = [1/2, 3/1, 8/4, 5/4, 1/3, etc.]
• Real numbers: They are represented with an "R", these include both rational numbers and irrational numbers. R = [Q, irrational]
• Complex numbers: They are represented with a "C", include all types of previous numbers plus the imaginary number "i". C = [N, Z, Q, R, i]

### Even numbers

Any integer that can be divided by 2, in other words would be to obtain half of a number with a residue of 0 or no decimal points. You can also identify an even number if the last digit or the unit is 0, 2, 4, 6 or 8. Example: 38 is an even number since the last digit is 8, if at 38 we divide it by 2 the result is 19, other even numbers: -20, 6, 16 and -34 are all even numbers.

### Odd numbers

An odd number can be easily identified if the last digit is 1, 2, 5, 7 or 9. Example: 35, 27, 49, and - 33 are odd numbers.

### Prime numbers

Prime numbers are numbers that are only divisible between themselves and 1.

### Numbers with decimals

They are numbers that have a decimal part.

### Ordinal numbers

They are those that denote a position of an element or set of elements in an ordered sequence.

### PI number

The number pi is the relationship between the perimeter of a circle and the length of its diameter, it is considered as an irrational number.

### Golden Number

The Golden number or gold number, is an irrational number, is a number that has many interesting properties.

### Euler Number

The Euler number is a mathematical constant and belongs to the most important irrational numbers.