You can calculate the sum of values of an expression F, depending on variable i , using function
sum(F,i,m,n)
m and n stand for minimal and maximal values of i. While calculating of the sum, variable of summation changes from m to n with increment 1.
When sum is being calculated variable of summation should not be defined.
Example
sum(n^2,n,1,10) ; result: 385.