Is to take out m different elements (0≤m≤n) from n different elements at a time, and combine them into a group in no particular order, which is called the combination of selecting m elements from n elements without repetition. The sum of all these combinations is called the number of combinations.
C(n, m) represents the number of combinations of n and m, which is equal to the product of m natural numbers decreasing continuously from n divided by the product of m natural numbers increasing continuously from 1.
Extended data
The calculation method of permutation and combination is as follows:
The arrangement A(n, m)=n×(n- 1). (n-m+ 1)=n！ /(n-m)！ (n is subscript and m is superscript, the same below)
Combination C(n, m)=P(n, m)/P(m, m) =n! /m！ (n-m)！ ;
For example:
A(4，2)=4！ /2! =4*3= 12
C(4，2)=4！ /(2! *2! )=4*3/(2* 1)=6