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121 (one hundred () twenty-one) is the natural number following 120 and preceding 122. ==In mathematics== One hundred () twenty-one is a square and is the sum of three consecutive primes (37 + 41 + 43). There are no squares besides 121 known to be of the form , where ''p'' is prime (3, in this case). Other such squares must have at least 35 digits. There are only two other squares known to be of the form n! + 1, supporting Brocard's conjecture. Another example of 121 being of the few examples supporting a conjecture is that Fermat conjectured that 4 and 121 are the only perfect squares of the form ''x''3 - 4 (with ''x'' being 2 and 5, respectively).〔Wells, D., ''The Penguin Dictionary of Curious and Interesting Numbers'', London: Penguin Group. (1987): 136〕 It is also a star number and a centered octagonal number. In base 10, it is a Smith number since its digits add up to the same value as its factorization (which uses the same digits) and as a consequence of that it is a Friedman number (11^2). But it can not be expressed as the sum of any other number plus that number's digits, making 121 a self 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「121 (number)」の詳細全文を読む スポンサード リンク
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