On Fri, Nov 20, 2009 at 13:06, Sasha Pachev <sasha at asksasha.com> wrote: > If you had a 64 bit number written down in hex, how could you quickly > tell without the aid of any computational device, including pencil or > paper if it is divisible by 15? > > How about 17? By 15 do you mean 15 or F? By 17 do you mean 17 or 11? -- Alan