Talk:Multiplication table

Using wikitext and wikitables

The first 2 multiplication tables are HTML tables, it is recommended to use wikitext and wikitables as much as possible with MediaWiki. Wikitables are lighter and simpler to edit. Especially, the two first multiplication tables could have their presentation optimized with wikitables.

Daniel Forgues 20:29, 30 August 2010 (UTC)

I would definitely change all tables that I've put in HTML format into wiki format, but, speaking only for myself, I don't consider it a high priority. Nonetheless I'm grateful for all your hard work in these unglamorous aspects, and I try to carry them over whenever practical (as I tried to do with the table of multiples which was based on the table for powers). Alonso del Arte 21:36, 30 August 2010 (UTC)

Multiplication triangle row sums give pentagonal pyramidal numbers

What am I doing wrong?

The pentagonal pyramidal numbers are obtained by a pyramid of pentagons

$\sum _{i=1}^{n}{\frac {i\,(3i-1)}{2}}={\frac {1}{2}}\left(3\sum _{i=1}^{n}i^{2}-\sum _{i=1}^{n}1\right)={\frac {1}{2}}\left({\frac {n(n+1)(2n+1)}{2}}-n\right)$

${\stackrel {?}{=}}\,n\,t_{n}={\frac {n^{2}(n+1)}{2}},$

where ${\frac {i\,(3i-1)}{2}}$ is the $i$th pentagonal number and $\sum _{i=1}^{n}i^{2}$ is the $n$th square pyramidal number.

— Daniel Forgues 19:27, 29 March 2014 (UTC)