Lời giải :
program hotrotinhoc ;
var a,b,i,dem : integer ;
kt : boolean ;
begin
kt:=true ;
write('a='); readln(a);
write('b='); readln(b);
if a=1 then kt:=false ;
dem:=0;
for i:= a to trunc(sqrt(b)) do
if b mod i = 0 then kt:= false ;
if kt = true then dem:=dem+1;
write('Co tat ca ',dem,' so nguyen to');
readln
end.