India, Feb. 9 -- A number of puzzles that have appeared in Problematics over the last three-and-a-half years have involved a magician playing tricks on a gullible audience, sometimes with cards, sometimes with matches, and sometimes simply with numbers. In most cases, it is not difficult to figure out how a given trick works.

You may agree, however, that most such tricks provide a lot of fun. For the magician, the fun lies in packaging his chosen mathematical principles into a trick that engages/enthralls his audience. For puzzlers, of course, the fun lies in going backwards and finding out how it's done. I think readers will enjoy this unusual little trick I came across very recently.

#Puzzle 181.1

Our magician asks you to think of an...