|Journal of Integer Sequences, Vol. 18 (2015), Article 15.6.6|
Department of Mathematics
Massachusetts Institute of Technology
Cambridge, MA 02139
Department of Mathematical Sciences
School of Science and Technology
Kwansei Gakuin University Sanda, Hyogo, 669-1337
Received October 13 2014; revised version received May 29 2015. Published in Journal of Integer Sequences, June 3 2015.