a)
program ct;
uses crt;
var n,S,i:integer;
begin
clrscr;
write('nhap n='); readln(n);
S:=0;
for i:=1 to n do S:=S+2*i;
writeln('tong=',S);
readln
end.
b)
program ct;
uses crt;
var n,S,i:integer;
begin
clrscr;
write('nhap n='); readln(n);
S:=0;
for i:=1 to n do S:=S+(2*i+1);
writeln('tong=',S);
readln
end.
c)
program ct;
uses crt;
var n,S,i:integer;
begin
clrscr;
write('nhap n='); readln(n);
S:=0;
for i:=1 to n do S:=S+i*(i+1);
writeln('tong=',S);
readln
end.
