hack? tsk tsk. if you get anything under 1000, it's probably quicker to subtract multiples of 70 until it gets to 2 digits - you should just memorize all the

hack? tsk tsk. if you get anything under 1000, it's probably quicker to subtract multiples of 70 until it gets to 2 digits - you should just memorize all the 2 digits multiples of 5,7,11,13, etc. Seriously, there aren't that many! for example, here's a quicker way for 1353 than what staticshock posted. 1353 - 1100 = 253. and 253 - 220 = 33. And clearly 11 divides 33, so 11 divides 1353. modular arithmetic ftw!