October 2018
Beginner
250 pages
12h 14m
English
Given a positive whole number
, the product of all the whole numbers from 1 up to
is called
factorial, denoted by the symbol
. In other words,
Also, by convention
, so
is defined for
. The sequence goes 1, 1, 2, 6, 24, 120, 720, 5040, 40320, …, and thereafter gets large very rapidly.
One may think of
as the number of different ways of picking objects one at a time from a basket containing
objects without replacing them. There are ways to pick the first one, ways to pick ...