freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-425-prime-connection.english.md

---
id: 5900f5151000cf542c510028
challengeType: 5
title: 'Problem 425: Prime connection'
---

## Description
<section id='description'>
Two positive numbers A and B are said to be connected (denoted by "A ↔ B") if one of these conditions holds:
(1) A and B have the same length and differ in exactly one digit; for example, 123 ↔ 173.
(2) Adding one digit to the left of A (or B) makes B (or A); for example, 23 ↔ 223 and 123 ↔ 23.


We call a prime P a 2's relative if there exists a chain of connected primes between 2 and P and no prime in the chain exceeds P.


For example, 127 is a 2's relative. One of the possible chains is shown below:
2 ↔ 3 ↔ 13 ↔ 113 ↔ 103 ↔ 107 ↔ 127
However, 11 and 103 are not 2's relatives.


Let F(N) be the sum of the primes ≤ N which are not 2's relatives.
We can verify that F(103) = 431 and F(104) = 78728.


Find F(107).
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler425()</code> should return 46479497324.
    testString: assert.strictEqual(euler425(), 46479497324, '<code>euler425()</code> should return 46479497324.');

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function euler425() {
  // Good luck!
  return true;
}

euler425();
```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```
</section>