5 (number)

5 (Somali: shan) is a natural number that falls between 4 and 6. It is an integer and is used both for counting and for ordinal purposes: 'shan wax' (five things) and 'shanaad' (fifth).

The numeral for 5 in the Hindu-Arabic numbering system is '5'. In Roman numerals it is written V, while in Eastern Arabic numerals it is written ٥. Many human counting systems, including the decimal system, are believed to derive from the number of fingers on one hand, which is five.

Mathematical properties

5 is a prime number — it has only two divisors, 1 and itself. It is the third prime number, after 2 and 3. It is also an odd number, since it cannot be divided by two.

In the decimal system, any number ending in 0 or 5 is divisible by 5. This makes 5 relatively easy to calculate mentally. Adding 5 to another number consistently changes the final digit in a predictable alternating pattern.

In geometry, five is the number of sides and vertices of a pentagon. There are also five Platonic solids — the tetrahedron, cube, octahedron, dodecahedron, and icosahedron — which are three-dimensional shapes whose faces are all identical.

Social and cultural use

Five is used as a grouping base in various aspects of daily life: counting fingers, dividing the hour into five-minute intervals, and many monetary values based on units of 5 and 10. In Somali, 'shan' is one of the basic numerals from 1 to 10 from which compound numbers are formed, such as 'shan iyo toban' (fifteen).