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 toCOMBIN(n+k1)
, which can be read as "(n+k1)choose k" or .COMBINA(n, k)
is also equivalent toFACT(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 the some of 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 