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Oliver Eyton-Williams 0bd52f8bd1 Feat: add new Markdown parser (#39800 )

and change all the challenges to new `md` format.

2020-11-27 10:02:05 -08:00

id, title, challengeType, forumTopicId

id	title	challengeType	forumTopicId
5900f5041000cf542c510016	Problem 407: Idempotents	5	302075

--description--

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.

--hints--

euler407() should return 39782849136421.

assert.strictEqual(euler407(), 39782849136421);

function euler407() {

  return true;
}

euler407();

// solution required