The COMBINA function returns the number of ways to choose some number of objects from a pool of a given size of objects, including ways to choose the same object multiple times (also known as choosing with replacement).
Parts of a COMBINA function
COMBINA(n, k)
Part  Description  Notes 
n 
The size pool of objects to choose from. 

k 
The number of objects to choose. 

Sample formulas
COMBINA(5, 3)
COMBINA(A1, B1)
Notes
 The order of the chosen objects within the COMBINA function doesn't matter.
COMBINA(n, k)
is equivalent to COMBIN(n+k1), which can be read as "(n+k1)choose k" or .COMBINA(n, k)
is also equivalent to FACT(n+k1)/(FACT(k)*FACT(n1)), but supports larger numbers as arguments. If a number (or reference to a number) with a decimal part is provided to COMBINA, the decimal part is silently truncated before calculation.
 If some of the arguments n+k is greater than or equal to 1031, a #NUM! error is returned.
Examples
In the following example with a pool of 2 objects (for example, A and B), there are 3 possible chosen combinations: (A, B), (A, A), and (B, B):
A  B  
1  Formula  Result 
2  =COMBINA(2, 2)  3 
In this example with a pool of 5 objects, there are 35 possible chosen combinations of 3 objects:
A  B  
1  Formula  Result 
2  =COMBINA(5, 3)  35 