citogenesis is the obvious answer

Luckily, "xkcd" doesn't refer to anything else than the comic AFAIK, so we can easily search and find that 143 English Wikipedia articles reference the comic. [0] Glossing over the list, I'd count 4 of these are directly referencing a specific comic or a concept invented in one: Time, Ballmer Peak, and Geohashing.

There are more if you include special pages, like Citogenesis reported by sibling.

The other way around, folks at the Explain xkcd wiki have categorized the comics and 56 of them reference Wikipedia. [1]

[0] https://en.wikipedia.org/w/index.php?title=Special:Search&fu...

[1] https://www.explainxkcd.com/wiki/index.php/Category:Wikipedi...

Hopefully none, since they don't meet Wikipedia's notability requirements and much more important things (such as places with thousands of people, and software with tens of thousands of users) have been rejected for not meeting the same requirements.

I wonder how many Wikipedia articles have XKCD comics?

Edit: I asked Opus 5.5, medium effort, and got a lame answer. Then asked it for "extra" effort, and the summary of that is:

WP->xkcd: Ballmer Peak, Geohashing, Time, a few other passing mentions

xkcd->WP: Missal of Silos, Rolle's Theorem, at least 54 other general references to WP