[dylandrop]

Trick: add up digits, if they are divisible by 3 so is the number. In this case 117 yields 1+1+7 = 9, and sure enough so is 117. (117 / 3 == 39).

https://en.wikipedia.org/wiki/Divisibility_rule#Divisibility...

[ilyanep]

Yeah, I had been doing that with other numbers, but somehow didn't trigger for that one. Must have been the timing pressure.