yaworsw/euler-manager

---
:id: 407
:name: Idempotents
:url: https://projecteuler.net/problem=407
:content: "If we calculate <var>a</var><sup>2</sup> mod 6 for 0 ≤ <var>a</var> ≤ 5
  we get: 0,1,4,3,4,1.\n\nThe largest value of <var>a</var> such that <var>a</var><sup>2</sup>
  ≡ <var>a</var> mod 6 is 4.  \nLet's call M(<var>n</var>) the largest value of <var>a</var>
  \\< <var>n</var> such that <var>a</var><sup>2</sup> ≡ <var>a</var> (mod <var>n</var>).
  \ \nSo M(6) = 4.\n\nFind ∑M(<var>n</var>) for 1 ≤ <var>n</var> ≤ 10<sup>7</sup>.\n\n"