uses crt;
var n,i:byte;
    s:longint;
BEGIN
        clrscr;
        write('Nhap n:'); readln(n);
        s:=0;
        for i:=1 to n do
        s:=s+ sqr(i);
        write('Tong S la:',s);
        readln
END.

Câu 1:

program tonglt;

uses crt;

var n,i:byte;

       tong:int64;

begin

clrscr;

write('Nhap n: ');   readln(n);

tong:=0;

for i:=1 to n do

 tong:=tong+i*i;

write('Tong la: ',tong);

readln(n);

end.   {n chi duoc be hon 20 thoi nha}

Câu 2:

program tinhtong;

uses crt;

var n,i:integer;

      tong:real;

begin

clrscr;

write('Nhap n: ');  readln(n);

tong:=0;

for i:=1 to n do

 tong:=tong+1/i;

write('Tong la: ',tong:2:3);

readln

end.

Câu 3: 

program tinhtong;

uses crt;

var i,n:integer;

      tong:int64;

begin

clrscr;

write('Nhap n: ');   readln(n);

tong:=0;

for i:=1 to n do

 tong:=tong+i*(i+1);

write('Tpng la: ',tong);

readln

end.

Câu 4:

program tinhtong;

uses crt;

var n,i:integer;

      tong:longint;

begin

clrscr;

write('Nhap n: ');   readln(n);

tong:=0;

for i:=1 to n do

 tong:=t+i;

writeln('Tong cac so nguyen tu 1-->',n,' la: ',tong);

tong:=0;

for i:=1 to n do

 if i mod 3=0 then tong:=tong+i;

write('Tong cac so chia het cho 3 tu 1-->',n,' la: ',tong);

readln

end.