This sequence is from September 2001 IBM "Ponder This" challenge. And it is missing in OEIS. Would anybody like to verify/extend/submit to OEIS? puzzle: http://domino.research.ibm.com/Comm/wwwr_ponder.nsf/challenges/September2001.html solution (containing the sequence): http://domino.research.ibm.com/Comm/wwwr_ponder.nsf/solutions/September2001.html Max