Sorry, but i think all above are wrong!! since they calculate some numbers twice!! between 1 and 100 we have 3,13,23,43,53,63,73,83,93 = 9 times and we have the numbers 30-39 = 10 times which gives us total of 19 nunbers!! (not 20) So between 0 and 1000 this metod will repeat itself 9 times for, 0-9...