Another trick: if the last 4 digits of the number are divisible by 16, the full number is divisible by 16. So far as I know, if the last X digits of a number are divisible by 2^X, the entire number is divisible by 2^X.
@James: nice trick! (and I guess the proof arises from 10^x being always exactly divisible by 2^x, so "iff" also applies?)
perhaps less interesting but I guess you could do the same with powers of 5, iff the last X digits of a number are divisible by 5^x, then the entire number is divisible by 5^x...
Remove all the words that end with "ain"
Energy of a photon
Set some matrix elements to zero
Insert zeros into vector
Fahrenheit to Celsius converter
Lights Out 5 - 5x5, 10 moves
Cycling — Critical Power
Divisible by 12
Lights Out 14 - 5x5, four stages, x moves
Lights Out 11 - 5x5, with wrapping, x moves
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