What does the letter of the number set in the first math class of senior one mean? For example, what are the letters of natural numbers and rational numbers? I forgot to bring my book and write all my letters. The set composed of all nonnegative integers is called nonnegative integer set (or natural number set), and is denoted as n; The set of all positive integers except zero is called positive integer set, and it is recorded as N* or N+(“+ ("+"(marked with "+"in the lower right corner); The set composed of all integers is called integer set, which is denoted as z; The set of all rational numbers is called rational number set, and it is recorded as q; The set composed of all real numbers is called real number set, which is marked as R, and the complex number set composed of all real numbers and imaginary numbers is called complex number set, which is marked as C: there are irrational number sets and so on.