43 lines
669 B
Markdown
43 lines
669 B
Markdown
---
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id: 5900f5041000cf542c510016
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title: 'Problem 407: Idempotents'
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challengeType: 5
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forumTopicId: 302075
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dashedName: problem-407-idempotents
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---
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# --description--
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If we calculate a2 mod 6 for 0 ≤ a ≤ 5 we get: 0,1,4,3,4,1.
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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.
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Find ∑M(n) for 1 ≤ n ≤ 107.
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# --hints--
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`euler407()` should return 39782849136421.
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```js
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assert.strictEqual(euler407(), 39782849136421);
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```
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# --seed--
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## --seed-contents--
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```js
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function euler407() {
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return true;
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}
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euler407();
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```
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# --solutions--
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```js
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// solution required
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```
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