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77 (seventy-seven) is the natural number following 76 and preceding 78. Seventy-seven is the smallest positive integer requiring five syllables in English. ==In mathematics== Seventy-seven is the 22nd discrete biprime and the first of the (7.q) family. Since both 7 and 11 are Gaussian primes, this means that 77 is a Blum integer. 77 has an aliquot sum of 19 and it is the second number to do so the first being 65; 77 is the 2nd member of the 19-aliquot tree. It is the sum of three squares, 42 + 52 + 62, as well as the sum of the first eight prime numbers. It also is the number of integer partitions of the number 12.〔(The On-Line Encyclopedia of Integer Sequences )〕 It is the largest number that cannot be written as a sum of distinct numbers whose reciprocals sum to 1.〔(Erich Friedman, Stetson University )〕 77 and 78 form a Ruth–Aaron pair. It is possible for a sudoku puzzle to have as many as 77 givens, yet lack a unique solution.〔(The Science behind Sudoku, J.P. Delahaye )〕 It and its ''sibling'' 49 are the only 2-digit numbers whose home primes (in base 10) have not been calculated. It is the number of digits of the 12th perfect number.〔(Mersenne Primes: History, Theorems and Lists )〕 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「77 (number)」の詳細全文を読む スポンサード リンク
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