freeCodeCamp/curriculum/challenges/chinese/10-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.md

---
id: 5900f4151000cf542c50ff28
title: >-
  Problem 169: Exploring the number of different ways a number can be expressed as a sum of powers of 2
challengeType: 5
forumTopicId: 301803
dashedName: >-
  problem-169-exploring-the-number-of-different-ways-a-number-can-be-expressed-as-a-sum-of-powers-of-2
---

# --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)?

# --hints--

`euler169()` should return 178653872807.

```js
assert.strictEqual(euler169(), 178653872807);
```

# --seed--

## --seed-contents--

```js
function euler169() {

  return true;
}

euler169();
```

# --solutions--

```js
// solution required
```