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# 13 (number)

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

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Cardinal | thirteen | |||

Ordinal |
13th (thirteenth) | |||

Factorization | prime | |||

Prime | 6th | |||

Divisors | 1, 13 | |||

Roman numeral | XIII | |||

Binary |
1101_{2} | |||

Ternary |
111_{3} | |||

Quaternary |
31_{4} | |||

Quinary |
23_{5} | |||

Senary |
21_{6} | |||

Octal |
15_{8} | |||

Duodecimal |
11_{12} | |||

Hexadecimal |
D_{16} | |||

Vigesimal |
D_{20} | |||

Base 36 |
D_{36} |

**Thirteen** is a number. It comes after twelve and before fourteen. It is an uneven number.

Many people think thirteen is an unlucky number, especially when it occurs on Friday the thirteenth day of the month. This is a superstition. There is no proof that thirteen is an unlucky number.

Floors in tall buildings often skip floor thirteen. The idea of thirteen as an unlucky number was created in Norse mythology. It is supposed to be unlucky to have thirteen people sitting at a table at a meal. Death is number thirteen in the tarot deck.

In Roman numerals, 13 is written as **XIII**.