121/120
In Just Intonation, 121/120 is a superparticular interval (the biyatisma) of around 17.4¢ which makes the difference between two undecimal neutral seconds of 11/10 and 12/11. Temperaments in which 121/120 is tempered out include 22edo, 31edo, 53edo and others; in such systems, 11/10 and 12/11 are equated. This is in contrast to the more familiar tempering out of 81/80, which results in meantone and other temperaments, in which 10/9 is equated with 9/8. Along with being the difference between 11/10 and 12/11, 121/120 is the difference between 11/8 and 15/11, so that tempering out 121/120 allows for the triad which has intervals of 11/8, 11/8, and 16/15.