#### The function COMBIN returns the number of ways a given number of items can be combined, without repetitions, into groups of a given size.

This function takes two Numbers as input: one gives the number of items that can be pulled from and combined, the other gives the number of items in each combination. It returns another Number: the number of different combinations that can be created given the constraints. A unique combination is defined only by which items are in it, not by how they might be arranged. Each item can only appear once in each combination.

### Declaration

COMBIN(items, chosen) -> number

### Parameters

**items**(required, type:*Number*)- The number of item that can be used to make new combinations.

**chosen**(required, type:*Number*)- The number of items that make up each combination.

### Return Values

**number**(type:*Number*)- The number of unique combinations that can be made given the number of items that can be used to make new combinations and the number of items that make up each combination.
- A unique combination is defined only by which items are in it, not by how they might be arranged. Each item can only appear once in each group.

### Examples

The following example calculates how many ways three items might be combined into groups of two. Note that each item can appear only once in each combination:

COMBIN(3, 2) -> 3

The following example calculates how many ways four different items might be combined in to groups of three. Note again that each item can appear only once in each combination.

COMBIN(4, 3) -> 4

### Discussion

The function COMBIN is similar to the function COMBINA, but with one crucial difference: the COMBINA functions returns the number of possible combinations assuming each item can appear multiple times in each combination, whereas the COMBIN function assumes each item can appear only once in each combination.