alt Hacker NewsDifferent cultures have different norms and rules. I think you're saying that, in your native language, they taught you not to use mathematical notation in prose.
They didn't teach you that about English, though. It's quite common to write "21x" for "21 times" in English and is pretty much universally understood and accepted by native speakers.
It's a more general rule about when and where to use mathematical notation. Though style rules do differ in places.
For what it's worth I've not seen "12x" in formal contexts, but if that is proper then the times symbol still shouldn't be styled as part of the maths formula imho.