There are also nifty little "tricks" that once learned can make the memorization easier:
ie: multiplied by one will be the original number; by two will always be an even number, by three, the sum of the digits will be divisible by 3; by 4 will be every "other" even number; by five will end in "0" or "5"; by nine, the sum of the digits will equal 9 (9x9=81; 8+1=9) (9x11=99; 9+9=18; 1+8=9); tens will always end in zero - there are "tricks" for them all. I wish I could include them all here, but a search of the web should prove fruitful. I hope you find this helpful! :)