Contrast with<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Digital_root" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Digital_root</a><p>which presents much of the same material and is a decent fully-wikified article using math notation.<p>I think the casting out nines article could be improved a lot, maybe with more of a focus on the history of the concept.