"Thirteen" redirects here. For other uses of "13" and "Thirteen", see 13
13 (thirteen) is the natural number after 12 and before 14. It is the smallest integer with eight letters in its spelled out name in English.
Thirteen is the 6th smallest prime number; the next is seventeen. 13 is the second Wilson prime. 13 is the fifth Mersenne prime exponent, yielding 8191.13 is the second star number and the seventh Fibonacci number. As it is an odd-indexed Fibonacci number, it is a Markov number, appearing in solutions to the Markov Diophantine equation: (1, 5, 13), (1, 13, 34), (5, 13, 194), ...There are 13 Archimedean solids.13 goes into 999,999 exactly 76,923 times, so vulgar fractions with 13 in the denominator have six digit repeating sequences in their decimal expansions. It is thus the smallest half period prime 13 is the largest number whose factorial is less than 1010. This means 13 is often the largest factorial a pocket calculator can represent without scientif