Definitions of classical constants and the imaginary unit

Classical constants and the imaginary unit include eight basic constants: golden ratio , pi , the number of radians in one degree , Euler number (or Euler constant or base of natural logarithm) , Euler-Mascheroni constant (Euler gamma) , Catalan number (Catalan's constant) , Glaisher constant (Glaisher-Kinkelin constant) , Khinchin constant (Khintchine's constant) , and the imaginary unit . They are defined by the following formulas:

The number is the ratio of the circumference of a circle to its diameter.