C++ Programming Exercise: Evaluate the sum of the following sequence

This exercise i got from Lecturer Bora (UBB). Let's go.
Code:
#include<iostream.h>
#include<conio.h>
void main(){
                clrscr();
                int i, s1, n;
                cout<<"Input value n:"; cin>>n;
                s1=0;
                for(i=1;i<=n;i++){
                                s1+=2*i;
                }
                cout<<"s1=2+4+...+2n= "<<s1<<endl;
                getch();
}
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            Code:
            #include<iostream.h>
            #include<conio.h>
            #include<math.h>
            void main(){
                         clrscr();
                         int i, n;
                         float s2;
                         cout<<"Input value n:"; cin>>n;
                         s2=0;
                         for(i=1;i<=n;i++){
                                   s2+=pow(-1,i-1)*(float)(3*i-1)/(float)(4*i+5);
                         }
                         cout<<"s2=2/9-5/13+8/17+...= "<<s2<<endl;
                         getch();

             }
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            Code:
            #include<iostream.h>
            #include<conio.h>
            #include<math.h>
            void main(){
                       clrscr();
                       int i, s3, n;
                       cout<<"Input value n:"; cin>>n;
                       s3=0;
                       for(i=1;i<=n;i++){
                       s3+=pow(-1,i-1)*pow(5,i);
                       }
                       cout<<"s3=5-5^2+5^3-...= "<<s3<<endl;
                       getch();
            }
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            Code:
#include<iostream.h>
#include<conio.h>
#include<math.h>
int factorial(int a){
                if(a==0) return 1;
                else return factorial(a-1)*a;
}
void main(){
                clrscr();
                int i, n;
                float s4;
                cout<<"Input value n:"; cin>>n;
                s4=0;
                for(i=1;i<=n;i++){
                 s4+=factorial(i)*sqrt(2*i);
                }
                cout<<"s4=1!sqrt(2)+2!sqrt(4)+...= "<<s4<<endl;
                getch();
}
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Code:
#include<iostream.h>
#include<conio.h>
void main(){
                clrscr();
                int i, n, s5;
                cout<<"Input value n:"; cin>>n;
                s5=0;
                for(i=1;i<=n;i++){
                 s5+=i*(i+1)*(i+2);
                }
                cout<<"s5= 1x2x3 + 2x3x4+... = "<<s5<<endl;
                getch();
}
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            Code:
#include<iostream.h>
#include<conio.h>
#include<math.h>
void main(){
                clrscr();
                int i, n, s6;
                cout<<"Input value n:"; cin>>n;
                s6=0;
                for(i=1;i<=n;i++){
                 s6+=2*pow(3,i-1);
                }
                cout<<"s6= 2+6+18+... = "<<s6<<endl;
                getch();
}
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            Code:
#include<iostream.h>
#include<conio.h>
#include<math.h>
void main(){
                clrscr();
                int i, n, s7;
                cout<<"Input value n:"; cin>>n;
                s7=0;
                for(i=1;i<=n;i++){
                 s7+=pow(10,i)-1;
                }
                cout<<"s7= 9+99+999+... = "<<s7<<endl;
                getch();
}
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            Code:
#include<iostream.h>
#include<conio.h>
float factorial(int a){
                if(a==0) return 1;
                else return factorial(a-1)*a;
}
void main(){
                clrscr();
                int i, n, s8;
                cout<<"Input value n:"; cin>>n;
                s8=0;
                for(i=1;i<=n;i++){
                 s8+=factorial(i);
                }
                cout<<"s8= 1!+2!+3!+...n! = "<<s8<<endl;
                getch();
}
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            Code:
#include<iostream.h>
#include<conio.h>
void main(){
                clrscr();
                int n, p1, i;
                cout<<"Input value n: "; cin>>n;
                p1=1;
                for(i=1;i<=n;i++){
                              p1*=4*i-3;
                }
                cout<<"p1 =1*5*9*...*(4n-3)= "<<p1<<endl;
                getch();
}
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            Code:
#include<iostream.h>
#include<conio.h>
int factorial(int a){
                if(a==0) return 1;
                else return factorial(a-1)*a;
}
void main(){
                clrscr();
                int number;
                cout<<"Input value n: "; cin>>number;
                cout<<"p1 ="<<number<<"! = "<<factorial(number)<<endl;
                getch();
}
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