Y n nth derivative. Golden ratio constant. In calculus which is all about finding slopes and areas you can imagine that e is a pretty important number.
Symbols save time and space when writing.
For symbols that are used only in mathematical logic or are rarely used see List of logic symbols. In calculus which is all about finding slopes and areas you can imagine that e is a pretty important number. 27182818284590452353602874713527 and more It is often called Eulers number after Leonhard Euler pronounced Oiler. Symbols save time and space when writing.