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260 (two hundred () sixty) is the magic constant of the ''n''×''n'' normal magic square and ''n''-queens problem for ''n'' = 8, the size of an actual chess board. 260 is also the magic constant of the Franklin magic square devised by Benjamin Franklin. The minor diagonal gives 260, and in addition a number of combinations of two half diagonals of four numbers from a corner to the center give 260. 260 may also refer to the years AD 260 and 260 BC. ==261–269== 261 = 32·29, lucky number, nonagonal number, Harshad number, unique period in base 2, number of possible unfolded tesseract patterns ---- 262 = 2·131, meandric number, open meandric number, untouchable number, happy number, palindrome number, semiprime ---- 263 prime, safe prime, happy number, sum of five consecutive primes (43 + 47 + 53 + 59 + 61), balanced prime, Chen prime, Eisenstein prime with no imaginary part, strictly non-palindromic number, Bernoulli irregular prime, Euler irregular prime, Gaussian prime, full reptend prime, Solinas prime, Ramanujan prime. ---- 264 = 23·3·11, Harshad number. If you take the sum of all 2-digit numbers you can make from 264, you get 264: 24 + 42 + 26 + 62 + 46 + 64 = 264. 132 and 396 share this property.〔Wells, D. ''The Penguin Dictionary of Curious and Interesting Numbers'' London: Penguin Group. (1987): 138〕 ---- 265 = 5·53, semiprime, lucky number, Padovan number, number of derangements of 6 elements, centered square number, Smith number, subfactorial 6. ---- 266 = 2·7·19, sphenic number, Harshad number, nontotient, noncototient, self number, repdigit in base 11 (222). 266 is also the index of the largest proper subgroups of the sporadic group known as the Janko group ''J''1. ---- 267 = 3·89, semiprime, the number of groups of order 64.〔(Number of groups of order ''n'' )〕 * 267 is also the area code for Pennsylvania, USA (Philadelphia area including its suburbs in eastern Montgomery County and most of Bucks County, overlays with 215) ---- 268 = 22·67, noncototient, untouchable number ---- 269 prime, twin prime with 271, sum of three consecutive primes (83 + 89 + 97), Chen prime, Eisenstein prime with no imaginary part, highly cototient number, strictly non-palindromic number, full reptend prime 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「260 (number)」の詳細全文を読む スポンサード リンク
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