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The Independent Culture
I SPOTTED Prof Mindwarp at the cash dispenser the other day and asked him how his finely honed mind managed to remember his PIN numbers. "Trivial," he said. "It's a four-digit perfect square - not beginning with zero, of course - and its square root is given by reversing its middle two digits."

"And do you use the same number for your other cash card?" I asked.

"Certainly not!" he replied. "Though that is also a four-digit perfect square, and I can tell you that it comprises four consecutive digits, though not in the right order, of course." What are the Prof's numbers? (Answer on Monday).

Yesterday's answer:

2+1 cross; 1 returns; 10+5 cross; 2 returns; 2+1 cross: Total time: 2+1+10+2+2 = 17 minutes.