The Excel GAMMA function returns the value of the Gamma Function, Γ(n), for a specified number, n.
Syntax:= GAMMA(number)
The GAMMA function syntax has the following arguments:
 Number Required. Returns a number.
Example: Let’s look at some Excel GAMMA function examples and explore how to use the GAMMA function as a worksheet function in Microsoft Excel:
Syntax: =GAMMA(A2)
Result: 9.513507699
Based on the Excel spreadsheet above, the following GAMMA examples would return:
Syntax: =GAMMA(A3)
Result: 1
Syntax: =GAMMA(A4)
Result: 0.886226925
Syntax: =GAMMA(A5)
Result: 52.34277778
Syntax: =GAMMA(A6)
Result: 1.329340388
Syntax: =GAMMA(A7)
Result: 0.267866129
Syntax: =GAMMA(A8)
Result: #NUM!
Syntax: =GAMMA(A9)
Result: #NUM!
Syntax: =GAMMA(A10)
Result: #NUM!
Note:
 Г(N+1) = N * Г(N)
 If Number is a negative integer or 0, GAMMA returns the #NUM! error value.

If Number contains characters that are not valid, GAMMA returns the #VALUE! error value.
 The Gamma Function, Γ(n), is calculated by the following formula: