The feature I most want from little languages like this is safety: in addition to restricting what it can do, I want to be able to take a snippet of untrusted code and execute it with a strict limit on how long it can take and how much memory it is allowed to use.
I want this so I can build features for end-users to provide snippets of code while knowing they won't be able to break anything, either accidentally or maliciously.
This is a surprisingly rare quality!
A common failure point here is allowing infinite loops ("while true") or allowing unbound mathematical operations, like powers or factorials of really large numbers.
APL-family languages have a long history of using the symbol / as "over"; a reduction adverb. The composition +/ for taking a sum is mutually intelligible in APL, J, K, and Goal. It's only a comment, in this case, if it is preceded by whitespace.
Is that not a pun on the use of "/" for division, and how it's often expressed in spoken English? It might still be a weird sense of priorities, but an historical one rather than a new one.
I wouldn't characterize languages in the K family as particularly focused on math. They have vectors, but do not have matrices or higher dimensional arrays, they don't have a built-in to compute factorials, binomial coefficients, roots of a polynomial or hypergeometric functions. And Ks do have dictionaries and tables. Maybe you're thinking of J or some dialects of APL?
That's great for Advent of Code and similar challenges where you have to do some ad-hoc input parsing but also super handy in general.