64/27
64/27 is the Pythagorean minor tenth. It is a stack of three perfect fourths, and is an octave larger than a pythagorean minor third.
| Interval information |
Trivia
This interval is a common ultrawide aspect ratio, often marketed as 21:9, which simplifies to 7:3. 64/27 differs from 21/9 by 64/63, the septimal comma.