ExpX? How is the math done?

The following is what my output has to be. Well, minus the numbers obviously. I have to enter an integer for x, than n and than get an answer. Now, I'm really confused. How exactly is the math done? If I enter 5 for x and 6 for n, how do I get 26.041666?

[phps-Computer:~] php% javac ExpX.java

[phps-Computer:~] php% java ExpX

enter an integer for x: 5

enter an integer for n: 6

E(5) using n =6 terms is: 26.041666666666668

[phps-Computer:~] php% java ExpX

enter an integer for x: 34

enter an integer for n: 3

E(34) using n =3 terms is: 578.0

[phps-Computer:~] php% java ExpX

enter an integer for x: 12

enter an integer for n: 9

E(12) using n =9 terms is: 10664.228571428572

[phps-Computer:~] php% java ExpX

enter an integer for x: 5

enter an integer for n: -4

service not available

[phps-Computer:~] php% java ExpX

enter an integer for x: 3

enter an integer for n: 6

E(3) using n =6 terms is: 2.025