65/64

In Just Intonation, 65/64, the wilsorma, is a superparticular interval of around 26.8¢, nearly a quarter of a semitone or eighth of a tone. It belongs to the 13-prime limit, which means that the highest prime in the ratio is 13. 65 is 5 times 13, which means that 65/64 can be treated as a harmonic 13th above a harmonic 5th or vice versa. It is the difference between 5/4 and 16/13; 8/5 and 13/8; 13/12 and 16/15; 15/8 and 24/13, 13/10 and 32/25; 20/13 and 25/16, and of course, infinitely many other pairs of just intervals.

See: Gallery of Just Intervals