13 (number)

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12 13 14
Cardinalthirteen
Ordinal13th
(thirteenth)
Numeral systemtredecimal
Factorizationprime
Prime6th
Divisors1, 13
Roman numeralXIII
Binary11012
Ternary1113
Quaternary314
Quinary235
Senary216
Octal158
Duodecimal1112
HexadecimalD16
VigesimalD20
Base 36D36

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

Many people think thirteen is an unlucky number, especially when Friday is 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, or reserve it for a mechanical floor. The idea of thirteen as an unlucky number is from pagan Norse mythology. It was believed to be unlucky to have thirteen people sitting at a table at a meal, and death is number thirteen in the tarot deck.

In Roman numerals, 13 is written as XIII.