Divisor chains (Pascal Zimmer)	Discuss about this problem
http://www.stetson.edu/~efriedma/mathmagic/1198.html http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=035280 Find the longest sequence of N terms so that every pair of consecutive terms have a factor in common.