3136/3125, the hemimean comma, or the didacus comma is a 7-limit comma measuring about 6.1 cents. It is the difference between five classic major thirds (5/4) and two subminor sevenths (7/4); it is also the difference between 126/125 (septimal semicomma), and 225/224 (septimal kleisma).
In the 2.5.7 subgroup, tempering out the comma leads to the rank-2 2.5.7 subgroup temperament didacus (a variant of hemithirds without a mapping for 3) with a generator of 28/25. In the full 7-limit (22.214.171.124), tempering it out leads to the rank-3 hemimean family of temperaments, which splits the syntonic comma into two equal parts, each representing 126/125~225/224. It also splits 5/4 into two equal parts, each representing 28/25. Typical edos tempering out the comma include 68, 80, 87, 99, 111, 118 and 130, and all of them tune both 126/125 and 225/224 to a single step. Smaller edos that temper out the comma are 19, 25, 31, 37, which temper out both 126/125 and 225/224, thus also 81/80, on the 126.96.36.199 subgroup.