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13 (thirteen ) is the natural number following 12 and preceding 14. In spoken English, the numbers 13 and 30 are often confused. When carefully enunciated, they differ in which syllable is stressed: 13 vs. 30 . However, in dates such as 1300 ("thirteen hundred") or when contrasting numbers in the teens, such as ''13, 14, 15,'' the stress shifts to the first syllable: 13 . Strikingly similar folkloric aspects of the number 13 have been noted in various cultures around the world: one theory is that this is due to the cultures employing lunar-solar calendars (there are approximately 12.41 lunations per solar year, and hence 12 "true months" plus a smaller, and often portentous, thirteenth month). This can be witnessed, for example, in the "Twelve Days of Christmas" of Western European tradition.〔Frazier, King of the Bean, and the Festival of Fools. Cited in Thompson, Tok. 2002. (The thirteenth number: Then, there/ here and now. ) 'Studia Mythological Slavica'' 5, 145–159.〕 ==In mathematics== The number 13 is the sixth prime number, and the smallest emirp (a prime that is a different prime when reversed).〔Wells, D. ''The Penguin Dictionary of Curious and Interesting Numbers'', London: Penguin Group. (1987): 67–71.〕 It is also a Fibonacci number, a happy number, the third centered square number, and one of only 3 known Wilson primes. Since 52 + 122 = 132, (5, 12, 13) forms a Pythagorean triple. There are 13 Archimedean solids, and a standard torus can be sliced into 13 pieces with just 3 plane cuts.〔 There are also 13 different ways for the three fastest horses in a horse race to finish, allowing for ties, a fact that can be expressed mathematically by 13 being the third ordered Bell number.〔.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「13 (number)」の詳細全文を読む スポンサード リンク
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