fix(challenge-md): Fix file names and preserve challenge order in meta.json

curriculum/challenges/en/08-coding-interview-prep/project-euler/problem-451-modular-inverses.en.md

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+---
+id: 5900f5311000cf542c510042
+challengeType: 5
+title: 'Problem 451: Modular inverses'
+---
+
+## Description
+<section id='description'>
+Consider the number 15.
+There are eight positive numbers less than 15 which are coprime to 15: 1, 2, 4, 7, 8, 11, 13, 14.
+The modular inverses of these numbers modulo 15 are: 1, 8, 4, 13, 2, 11, 7, 14  
+because
+1*1 mod 15=1
+2*8=16 mod 15=1
+4*4=16 mod 15=1
+7*13=91 mod 15=1
+11*11=121 mod 15=1
+14*14=196 mod 15=1
+
+Let I(n) be the largest positive number m smaller than n-1 such that the modular inverse of m modulo n equals m itself.
+So I(15)=11.
+Also I(100)=51 and I(7)=1.
+
+Find ∑I(n) for 3≤n≤2·107
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+- text: <code>euler451()</code> should return 153651073760956.
+  testString: 'assert.strictEqual(euler451(), 153651073760956, ''<code>euler451()</code> should return 153651073760956.'');'
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function euler451() {
+  // Good luck!
+  return true;
+}
+
+euler451();
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+// solution required
+```
+</section>