[seqfan] Knight's tour on infinite board

[Neil Sloane]

Dear SeqFans, A068608-A068615 claim to give the 8 ways of making a knight's
tour of the doubly-infinite chessboard (the Z X Z board). There is a link
to a page of Frank Ellermann, but I did not see any definition of these
sequences.  What is the construction? And are there really only 8 solutions?

Best regards
Neil

Neil J. A. Sloane, President, OEIS Foundation.
11 South Adelaide Avenue, Highland Park, NJ 08904, USA.
Also Visiting Scientist, Math. Dept., Rutgers University, Piscataway, NJ.
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Email: njasloane at gmail.com