b)

uses crt;

var n,i:word;

    kq:longint;

BEGIN

        clrscr;

        write('Nhap N:'); readln(n);

        kq:=0;

        for i:=1 to n do

        kq:=kq+(i*i);

        write(kq);

        readln

END.

c)

uses crt;

var n,i:word;

    kq:real;

BEGIN

        clrscr;

        write('Nhap N:'); readln(n);

        kq:=0;

        for i:=1 to n do

        kq:=kq+1/i;

        write(kq:0:3);

        readln

END.

d)

uses crt;

var n,i:word;

    kq:qword;

BEGIN

        clrscr;

        write('Nhap N:'); readln(n);

        kq:=1; i:=3;

        while i<=(2*n+1) do

        begin

                kq:=kq*i;

                inc(i,2);

        end;

        write(kq);

        readln

END.

Chúc bạn học tốt!

b) 

var i, S, n : integer;

begin

write ('Nhap n la:'); readln(n);

S := 0;

for i := 1 to n do S := S + sqr(i); 

writeln('Tong la:', S);

readln

end.

c)

var i, n: byte;
     S: real;
begin
write ('Nhap n la:'); readln(n);
S := 0;
for i := 1 to n do S := S + 1/i;
writeln('Tong la:', S:3:2);
readln
end.

d)

var i, S, n : integer;
begin
write ('Nhap n la:'); readln(n);
S := 1;
for i := 1 to n do if i mod 2 <> 0 then S := S*i;
writeln('Tich la:', S);
readln
end.