The formula for calculating the combination number is
n
Meta set
A
Non-repetitive extraction
m
The combination of elements is essentially
A
one of
m
Meta subset sum. If a given set
A
sequencing
Let's turn it into an orderly collection
A
Intermediate extraction
m
The combination of elements corresponds to several segments.
Ordered set
A
Strict order-preserving mapping of. Number of combinations
Commonly used symbols are
Extended data:
1, complementary property, that is, the number of combinations of m elements taken from n different elements = taken from n different elements.
(noun-noun)
The nature of element combination number is easy to understand, such as c (9,2) = c (9,7), that is, the method of selecting two elements from nine elements is equal to the method of selecting seven elements from nine elements. Provisions: C(n, 0)= 1
C(n，n)= 1
C(0，0)= 1
2. If the combinatorial identity is expressed as
n
Select from the project
m
If the following formula exists: c (n, m) = c (n, n-m) = c (n- 1, m- 1)+c (n- 1, m).
References:
Baidu encyclopedia-combination number