4

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Algund Dominikanerinnenklosterkirche Portal bezeichnet 1481 (cropped)

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Seven-segment 4

Mugs of tea viewed from above

4 is a number, numeral, and digit. It is the natural number following 3 and preceding 5. It is the smallest composite number, its proper divisors being 1 and 2.

Mathematics[edit | edit source]

In mathematics, the number 4 is significant in various ways:

It is the smallest composite number.
It is the smallest square number (2^2).
It is the only number with the same number of letters as its value in the English language.
It is the second Fermat prime.
It is the second square number.

Properties[edit | edit source]

4 is the smallest number of sides of a polygon (a quadrilateral).
It is the smallest number of vertices of a polyhedron (a tetrahedron).
It is the smallest number of dimensions of a hypercube.

Science[edit | edit source]

In science, the number 4 has various applications:

There are four fundamental forces in physics: gravitational force, electromagnetic force, strong nuclear force, and weak nuclear force.
There are four nucleotide bases in DNA: adenine, cytosine, guanine, and thymine.

Culture[edit | edit source]

In various cultures, the number 4 holds different significances:

In Chinese culture, the number 4 is considered unlucky because it sounds like the word for "death" (死, pinyin: sǐ).
In Western culture, the number 4 is often associated with stability and order, as seen in the four seasons, four cardinal directions, and four elements (earth, water, air, fire).