Z Integer set When Nott introduced the concept of integer ring (integer set itself is also a number ring), she was German, and the integer in German was called Zahlen, so she recorded the integer ring as Z at that time, and the integer set was represented by Z from then on. The English word for integer is integer. See:/s/blog _ 5018d611kloc-0/00en9s.html for details.

Q rational number set because the result (quotient) of comparing two integers is called rational number, and the English of quotient is quotable, so Q is used. Rational numbers are rational numbers in English.

R set of real numbers

Complex number of c complex set