https://answers.yahoo.com/question/index?qid=20130519114338AAziTPE
Start with 100-999
eliminate 700-999, leaving 100-699
eliminate anything ending in 70-79,80-89,90-99, leaving 100-169,200-269,300-369,400-469,500-569,...
eliminate anything ending in 7,8,9. leaving 100-106,110-116,120-126,130-136,140-146,... through 666...49x6=294