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Thirteen (13) is the natural number following twelve and preceding fourteen. It is a Fibonacci number.

Thirteen is the 6th smallest prime number, the next is seventeen.

13 goes into 999,999 exactly 76,923 times, so fractions with 13 in the denominator have six digit repeating sequences in their decimal expansions.

In base fourteen and higher bases (such as hexadecimal), thirteen is represented as D.

Thirteen is also:

Strauss and Howe named Generation X the "Thirteenth Generation".

The "13" on a Hell's Angel's patch or tattoo refers to the thirteenth letter of the alphabet, M, for "marijuana".

There are 13 steps on the pyramid on the back of the American 1 Dollar Bill

Some theories of relativity state that there are 13 dimensions.

There were 13 Plutonium slugs in Fat Man, the atomic bomb dropped on Nagasaki.

See also: eleven, twelve, thirteen, fourteen, fifteen integer, list of numbers.

This article is about the number. For the year AD 13, see 13.