Dubs checking algos.

Post your dubs-checking algorithms. We have a lot spread out but it might be nice to collect all the good ones in a single thread. Revised version of an earlier one I wrote:

Number isDubs := method(
if(self toBase(11) asNumber mod(10) == 0,
Exception raise("checkem"); true,
false))

So Io doesn't even have immutable variables? How pathetic.