Taking out any m(m≤n) elements from N different elements and grouping them is called taking out the combination of M elements from N different elements; The number of all combinations of m(m≤n) elements from n different elements is called the number of combinations of m elements from n different elements.

For example: c (3,6) = (3 * 2 *1)/(6 * 5 * 4)

Combination is one of the important concepts in mathematics. Taking out m different elements from n different elements at a time, regardless of the order, is called choosing the combination of m elements from n elements without repetition. The number of species in all such combinations is called the combination number.

The formula for calculating the combination number is

The combination obtained by repeatedly extracting m elements from N-ary set A is essentially the sum of M-ary subsets of A. If ordered set A becomes an ordered set, then the combination of M elements extracted from A corresponds to some strict order-preserving mapping from several fragments to ordered set A. ..

What are the common symbols of combination numbers? 、

References:

Baidu encyclopedia-combination number