For any number x:

x 1 = 1 x = x

x/ 1 = x

x 1 = x

1x = 1

X@ 1 = x and 1@x = 1

For any number x, when x is not 0, x0= 1 note 1.

As a natural number, 1 is neither a prime number nor a composite number.

square number

Composite number of the first 1 height

Total hash number 1

The 1 lucky number

Triangular number

Rectangular number

Items 2 and 3 of Fibonacci sequence.

1 cannot be the base of logarithm.

The reciprocal of 1 is itself.

In factorial, 0! = 1! = 1

In probability theory, the probability of random events in any sample space is defined as 1.

1 is a positive number, integer, smallest positive integer, odd number, real number, rational number and algebraic number.

In geometry, the radius of the unit circle is 1.

In the field of science,

In computer science, 1 is often used to represent the "true" value in the truth table of Boolean logic.

In geometrical optics, the refractive index of vacuum is 1.

Astronomically, the average distance between the sun and the earth is 1 astronomical unit.

In chemistry, the atomic number of hydrogen is 1.

0.999...= 1

[Editor] In human culture

In Chinese dictionaries based on radical index, "one" is often the first radical and the first word.

In human culture, the word "one" gives the meaning of the beginning of all things: "Tai Chi is the only beginning, Tao stands in one, heaven and earth are divided into all things, and all things are unified" (Shuo Wen Jie Zi).

In English, "freshman" is also used to refer to the Lord God in the Bible.

The basic denomination of currency, such as USD 1, NT 1 Yuan.

In music theory, the do sound on the score is represented by 1.