The COMBIN function returns the number of ways to choose some number of objects from a pool of a given size of objects.
n- The size of the pool of objects to choose from.
k- The number of objects to choose.
COMBINis the standard combinatorics function typically notated nCk and read "n choose k". This is equivalent to
MULTINOMIAL: Returns the factorial of the sum of values divided by the product of the values' factorials.
FACTDOUBLE: Returns the "double factorial" of a number.
FACT: The FACT function returns the factorial of a number.