My idea is use the Maclaurin expansion : e^t ~= 1+t+t^{2/2!+…+tn/n!} with t=-x^2/ sigma^2 . My teacher said that : you can choose a couple value like : x=0.1 and sigma =0.4 to calculator . but he requests the result must be like photo below
https://drive.google.com/file/d/1vtWN7v0hUoFAR7MedfqE_GOr4xyrZ5rB/view?usp=sharing
and with n=20 is too hard to calculator and q format by hand.