Examples of exceptional objects.
Contains the first sporadic groups discovered by far: 11 and 12 in 1861, and 22, 23 and 24 in 1973. And therefore presumably the simplest! The next sporadic ones discovered were the Janko groups, only in 1965!
Each is a permutation group on elements. There isn't an obvious algorithmic relationship between and the actual group.
TODO initial motivation? Why did Mathieu care about k-transitive groups?
Their; k-transitive group properties seem to be the main characterization, according to Wikipedia:
  • 22 is 3-transitive but not 4-transitive.
  • four of them (11, 12, 23 and 24) are the only sporadic 4-transitive groups as per the classification of 4-transitive groups (no known simpler proof as of 2021), which sounds like a reasonable characterization. Note that 12 and 25 are also 5 transitive.
Looking at the classification of k-transitive groups we see that the Mathieu groups are the only families of 4 and 5 transitive groups other than symmetric groups and alternating groups. 3-transitive is not as nice, so let's just say it is the stabilizer of and be done with it.
Video 1. Mathieu group section of Why Do Sporadic Groups Exist? by Another Roof (2023) Source. Only discusses Mathieu group but is very good at that.
TODO why do we care about this?
Note that if a group is k-transitive, then it is also k-1-transitive.
TODO this would give a better motivation for the Mathieu group
www.maths.qmul.ac.uk/~pjc/pps/pps9.pdf mentions:
The automorphism group of the extended Golay code is the 54-transitive Mathieu group . This is one of only two finite 5-transitive groups other than symmetric and alternating groups
Hmm, is that 54, or more likely 5 and 4?
Video 1. Group theory, abstraction, and the 196,883-dimensional monster by 3Blue1Brown (2020) Source. Too basic, starts motivating groups themselves, therefore does not give anything new or rare.
TODO clickbait, or is it that good?