64/33

64/33, the undecimal suboctave, or octave-reduced 33rd subharmonic, is an interval which differs by a keenanisma (385/384) from the septimal suboctave. Just as with its octave compliment 33/32, this interval can potentially be treated as an interval in its own right, in which case it could be analysed as the undecimal supermajor seventh.