I would consider what you described to be "algorithms" (or "complexity theory"), a particular sub-area of computer science. There are quite a few other areas of CS.
The ACM organizes a number of SIGs (Special Interest Groups), each with their own (often several) conferences [1]. Some of the more well-known SIGs include SIGPLAN (Programming Languages), SIGGRAPH (Computer Graphics), and SIGLOG (Logic and Computation). What you described probably falls best under SIGACT (Algorithms and Computation Theory).
> the mathematics behind counting.
Traditionally, this is combinatorics, not any particular part of computer science. Complexity theory concerns itself with specifically counting the amount of resources used by a formal process.
The ACM organizes a number of SIGs (Special Interest Groups), each with their own (often several) conferences [1]. Some of the more well-known SIGs include SIGPLAN (Programming Languages), SIGGRAPH (Computer Graphics), and SIGLOG (Logic and Computation). What you described probably falls best under SIGACT (Algorithms and Computation Theory).
> the mathematics behind counting.
Traditionally, this is combinatorics, not any particular part of computer science. Complexity theory concerns itself with specifically counting the amount of resources used by a formal process.
[1] https://www.acm.org/special-interest-groups/alphabetical-lis...