R is the set of real numbers. Z is the set of integers {.., -2, -1, 0, 1, 2, ...}. Z is called "Z" due to influential German mathematicians who chose the lett

R is the set of real numbers. Z is the set of integers {.., -2, -1, 0, 1, 2, ...}. Z is called "Z" due to influential German mathematicians who chose the letter to stand for "zahlen" ("number" in German). As a fun fact, the letter "N" stands for "natural numbers," meaning either positive integers, or positive integers and zero. However, that letter (N) is _not_ standardized because mathematicians disagree about whether or not to include zero. When I separately told a couple of my professors this in grad school, they didn't believe me — one of them thinking it was crazy for zero to be excluded, the other thinking it was crazy to include it! https://en.wikipedia.org/wiki/Natural_number https://en.wikipedia.org/wiki/Natural_number