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126 (one hundred () twenty-six) is the natural number following 125 and preceding 127. ==In mathematics== As the binomial coefficient , 126 is a central binomial coefficient〔 See also OEIS:A001700 for the odd central binomial coefficients.〕 and a pentatope number.〔; 〕 It is also a decagonal number〔, pp. 2–3 and 6; 〕 and a pentagonal pyramidal number.〔, pp. 93, 211. 〕 As 125 + 1 it is σ3(5), the fifth value of the sum of cubed divisors function, and is a sum of two cubes. There are exactly 126 crossing points among the diagonals of a regular nonagon, 126 binary strings of length seven that are not repetitions of a shorter string, 126 different semigroups on four elements (up to isomorphism and reversal), and 126 different ways to partition a decagon into even polygons by diagonals. There are exactly 126 positive integers that are not solutions of the equation : where ''a'', ''b'', ''c'', and ''d'' must themselves all be positive integers.〔. See OEIS:A027563 for the list of these 126 numbers.〕 It is the fifth Granville number, and the third such not to be a perfect number. Also, it is known to be the smallest Granville number with three distinct prime factors, and perhaps the only such Granville number.〔J. D. Koninck, Those Fascinating Numbers, transl. author. American Mathematical Society (2008) p. 40.〕 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「126 (number)」の詳細全文を読む スポンサード リンク
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