I do this as a performance piece, in particular, performing it at this year's annual MathsJam gathering[0]. I do know people who have worked out how to do it from first principles. I became aware of it about 18 months ago, interesting to see it getting some publicity. I've been trying, but as yet have been unable to find the original source.<p>Tanya Khovanova[1] wrote about it some time ago, although I can't find the exact link, but doesn't remember where she got it from.<p>Nice puzzle.<p>[0] <a href="http://www.mathsjam.com" rel="nofollow">http://www.mathsjam.com</a><p>[1] <a href="http://blog.tanyakhovanova.com/" rel="nofollow">http://blog.tanyakhovanova.com/</a>