---
id: 5900f4ed1000cf542c50ffff
challengeType: 5
title: 'Problem 383: Divisibility comparison between factorials'
forumTopicId: 302047
---

## Description
<section id='description'>
Let f5(n) be the largest integer x for which 5x divides n.
For example, f5(625000) = 7.



Let T5(n) be the number of integers i which satisfy f5((2·i-1)!) < 2·f5(i!) and 1 ≤ i ≤ n.
It can be verified that T5(103) = 68 and T5(109) = 2408210.



Find T5(1018).
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler383()</code> should return 22173624649806.
    testString: assert.strictEqual(euler383(), 22173624649806);

```

</section>

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

<div id='js-seed'>

```js
function euler383() {
  // Good luck!
  return true;
}

euler383();
```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```

</section>