[saulpw]

My criteria are "no letters or digits from any language" (other than 2). So you can't use the log or S() or the gamma function, but you can use sqrt, because there is accepted symbology that does not require any atom of non-mathematical language to represent.

[Karellen]

What if it turns out that the radical (square root) symbol is a letter from a language (if a little squished)? And we somehow figure out one day which letter it is, for sure?

https://en.wikipedia.org/wiki/Radical_symbol#Origin

[pyrale]

APL programmers enter the room