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curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-242-odd-triplets.md

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+---
+id: 5900f45f1000cf542c50ff71
+challengeType: 5
+title: 'Problem 242: Odd Triplets'
+forumTopicId: 301889
+---
+
+## Description
+<section id='description'>
+Given the set {1,2,...,n}, we define f(n,k) as the number of its k-element subsets with an odd sum of elements. For example, f(5,3) = 4, since the set {1,2,3,4,5} has four 3-element subsets having an odd sum of elements, i.e.: {1,2,4}, {1,3,5}, {2,3,4} and {2,4,5}.
+
+When all three values n, k and f(n,k) are odd, we say that they make
+an odd-triplet [n,k,f(n,k)].
+
+There are exactly five odd-triplets with n ≤ 10, namely:
+[1,1,f(1,1) = 1], [5,1,f(5,1) = 3], [5,5,f(5,5) = 1], [9,1,f(9,1) = 5] and [9,9,f(9,9) = 1].
+
+How many odd-triplets are there with n ≤ 1012 ?
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>euler242()</code> should return 997104142249036700.
+    testString: assert.strictEqual(euler242(), 997104142249036700);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function euler242() {
+
+  return true;
+}
+
+euler242();
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+// solution required
+```
+
+</section>