This website is a semi-functional mirror of the original Project Euler. More information is available on GitHub.
projecteuler.net

Idempotents

Problem 407

Published on 23 December 2012 at 10:00 am [Server Time]

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.


Answer:
Go to back to Problems