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220 (two hundred () twenty) is the natural number following 219 and preceding 221. ==In mathematics== It is a composite number, with its divisors being 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110, making it an amicable number with 284.〔Bryan Bunch, ''The Kingdom of Infinite Number''. New York: W. H. Freeman & Company (2000): 167〕 Every number up to 220 may be expressed as a sum of its divisors, making 220 a practical number. Also, being divisible by the sum of its digits, 220 is a Harshad number. It is the sum of four consecutive primes (47 + 53 + 59 + 61). It is the smallest even number with the property that when represented as a sum of two prime numbers (per Goldbach's conjecture) both of the primes must be greater than or equal to 23. There are exactly 220 different ways of partitioning 64 = 82 into a sum of square numbers. It is a tetrahedral number, the sum of the first ten triangular numbers, and a dodecahedral number. If all of the diagonals of a regular decagon are drawn, the resulting figure will have exactly 220 regions. 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「220 (number)」の詳細全文を読む スポンサード リンク
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