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freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-169-exploring-the-number-of-different-ways-a-number-can-be-expressed-as-a-sum-of-powers-of-2.english.md
Valeriy 79d9012432 fix(curriculum): quotes in tests (#18828)
* fix(curriculum): tests quotes

* fix(curriculum): fill seed-teardown

* fix(curriculum): fix tests and remove unneeded seed-teardown
2018-10-20 23:32:47 +05:30

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---
id: 5900f4151000cf542c50ff28
challengeType: 5
title: 'Problem 169: Exploring the number of different ways a number can be expressed as a sum of powers of 2'
---
## Description
<section id='description'>
Define f(0)=1 and f(n) to be the number of different ways n can be expressed as a sum of integer powers of 2 using each power no more than twice.
For example, f(10)=5 since there are five different ways to express 10:
1 + 1 + 8
1 + 1 + 4 + 41 + 1 + 2 + 2 + 4
2 + 4 + 4
2 + 8
What is f(1025)?
</section>
## Instructions
<section id='instructions'>
</section>
## Tests
<section id='tests'>
```yml
tests:
- text: <code>euler169()</code> should return 178653872807.
testString: assert.strictEqual(euler169(), 178653872807, '<code>euler169()</code> should return 178653872807.');
```
</section>
## Challenge Seed
<section id='challengeSeed'>
<div id='js-seed'>
```js
function euler169() {
// Good luck!
return true;
}
euler169();
```
</div>
</section>
## Solution
<section id='solution'>
```js
// solution required
```
</section>