Idempotents
Problem 407
Published on Sunday, 23rd December 2012, 10:00 am; Solved by 617
If we calculate a2 mod 6 for 0 
a 5 we get: 0,1,4,3,4,1.
The largest value of a such that a2 
a mod 6 is 4.
Let's call M(n) the largest value of a 
n such that a2 a (mod n).
So M(6) = 4.
Find 
M(n) for 1 n 107.