What is the suffix in indexed math symbols

I've been watching some online courses and I'm having a difficulty understanding what exactly are they saying. The courses are scientific in nature and rather often an indexed symbols appear. The indexed symbols are usually written with a subscript, like this:

When refering to those, the instructor pronounced them like you would pronounce "ace of n" and "eyes of c". It seems that the suffix s is added to the letter. I have completed a non-English education, so this was new to me.

What are the rules regarding indexed symbols?

Is it simply: a's of n, or i's of c, and more importantly why?

Solution 1:

You are mishearing the instructor. He is saying "a sub n" and "i sub c", where "sub" is short for "subscript".

If the symbols are written with a superscript, like aⁿ and I^c, then the spoken version is "a sup n" and "i sup c", where "sup" is pronounced like "soup", and is short for "superscript".