9801/9800, the kalisma or Gauss' comma, is an 11-limit unnoticeable comma measuring about 0.18 cents. It is the smallest 11-limit superparticular interval. It can be described as the difference between 99/98 and 100/99, and between 99/70 and its octave complement, 140/99.
It factors into the two smallest 13-limit superparticular commas: 9801/9800 = 10648/10647 × 123201/123200.
Tempering it out leads to the kalismic temperament, which splits the octave into two equal parts, each representing 99/70~140/99. Odd edos cannot temper it out. See Rank-4 temperament #Kalismic (9801/9800) for some technical details.