# Page not found - BBC

**URL:** <https://forums.kodeco.com/t/page-not-found-bbc/199854>\
**Category:** Swift Apprentice: Fundamentals\
**Created:** [November 27, 2023, 1:23am UTC](https://forums.kodeco.com/t/page-not-found-bbc/199854 "2023-11-27T01:23:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![abilgin88](https://s3.amazonaws.com/cdn.raywenderlich.com/community/forum-assets/noun-game-ghost-878668.png) [@abilgin88](https://forums.kodeco.com/u/abilgin88)\
**Post date:** [November 27, 2023, 1:23am UTC](https://forums.kodeco.com/t/page-not-found-bbc/199854/1 "2023-11-27T01:23:07Z")

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**Note** : If you’re mathematically astute, you might notice that this example computes **triangle numbers**. Here’s a quick explanation: [http://bbc.in/1O89TGP](http://bbc.in/1O89TGP)  
the link is not provide anything about like " Sorry, but we’re having difficulties showing you the page you asked for."

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<div class="post-metadata">

**Author:** ![joshuk](https://s3.amazonaws.com/cdn.raywenderlich.com/community/forum-assets/noun-game-ghost-878668.png) [@joshuk](https://forums.kodeco.com/u/joshuk)\
**Post date:** [November 30, 2023, 8:20pm UTC](https://forums.kodeco.com/t/page-not-found-bbc/199854/2 "2023-11-30T20:20:47Z")

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I think it was a BBC Bitesize link which has been moved/removed by the BBC.

Here’s a youtube video explaining the concept and also a mathsisfun link

[![](https://img.youtube.com/vi/X3_h4w3jVsk/maxresdefault.jpg "Triangular Numbers - Corbettmaths") ](https://www.youtube.com/watch?v=X3_h4w3jVsk)

> **[Triangular Number Sequence](https://www.mathsisfun.com/algebra/triangular-numbers.html)**
>
> The Triangular Number Sequence comes from a pattern of dots that form a triangle