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The 638 equal temperaments divide the octave into 638 equal parts of 1.881 cents each. It tempers out the minortone comma, | -16 35 -17 >, in the 5-limit, 4375/4374 in the 7-limit, 43923/43904, 3025/3024, 9801/9800 in the 11-limit, and 625/624, 729/728, 1575/1573, 2200/2197 and 4225/4224 in the 13-limit. It supplies the optimal patent val for quatracot temperament. 638 factors as 2*11*29.