| |
|
| 13 | |
|---|---|
| Cardinal | thirteen |
| Ordinal | thirteenth |
| Factorization | prime number |
| Roman numeral | XIII |
| Binary | 1101 |
| Hexadecimal | D |
Mathematics
Thirteen is the 6th smallest prime number, the next is seventeen.
It is a Fibonacci number.
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 by the letter D.
Other fields
Regarded as an unlucky number in many cultures. Unreasoned fear of the number 13 is termed triskaidekaphobia. Due to this fear, some tall buildings have resorted to skipping the thirteenth floor or having a 12a-th floor instead. The thirteenth of a month is likewise ominous, at least when it falls on a Friday (see Friday the 13th). The 13th falls on a Friday more often than any other day. In fact it occurs more often than any other day/number combination except those that coincide with it (Thursday the 12th, Saturday the 14th, etc).
In the Christian religion, the number is considered significant since there were thirteen present at the Last Supper. Also, if both Judas and Matthias are counted, there were thirteen apostles. Thirteen was also once associated with the Epiphany by Christians, the Christ child having received the Magi on his thirteenth day of life.
Regarded as a lucky number in China because it is synonymous with '實生'; which means "must be alive". However 13 is regarded as unlucky by those Chinese under the influence of foreign cultures.
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".
Thirteen is:
12 and 14