You've got a clock that goes to 12. In step increments you can go 1, 2, 3, 4, 6 or 12 at a time to end up back at 12. These are the subgroups of 12. Now take the totient of 1, 2, 3, 4, 6, 12 equal to 1, 1, 2, 2, 2, 4. These are the number of elements in each subgroup. Add them together and what do you get? 1 + 1 + 2 + 2 + 2 + 4 = 12. This holds for any integer, not just 12.
But what if you want to make sure you hit every number on your clock rather than skipping over, for instance, 1, 3, 5, 7, 9 and 11?
There are 4 ways to do that, which is the essence of the term automorphism aka "self-mapping." You can step forward by 1 or 7 and back by 1 or 7, which is the same as stepping back by 5 or 11 or forward by 5, or 11. Thus, 1, 5, 7, 11.
This fact underlies the maths of the Circle of Fifths of the Western Musical System which is based on the Perfect 5th. 12 steps, 7 notes at a time and there you are, from C through G, D, A, E, B, F# etc. and back to C after 84 notes.
I'll take a look at the link you posted, but, in short, the mathematics of Automorphism Group Z(12) underlies all of Western Music. Think about that in relation to what you posted:
Z/24Z
(s+k)^2 = {01,09,16,12,01,09,04,00}
s^2 = {00,04,09,01,12,16,09,01}
n = {01,05,07,11,13,17,19,23}
Restate n...
n = 1, 5, 7, 11, 24 - 11, 24 - 7, 24 - 5, 24 - 1
Two times, not 1 time, around the clock for a 720 degree rotation comprised of 168 notes, "coincidentally" the number of symmetries associated with the Fano plane. Whoever thought to divide the day and week the way it's divided, I might add, seems to have been a natural group theorist.
- AC