OFFSET
1,3
COMMENTS
See the pdf file of the Curtis et al. reference for precise definition.
LINKS
Frank Curtis, John Drew, Chi-Kwong Li and Daniel Pragel, Central groupoids, central digraphs, and zero-one matrices A satisfying A^2 = J, Journal of Combinatorial Theory, Series A, Volume 105 Issue 1, (2004) pp. 35-50.
F. Curtis, J. Drew, Central groupoids, central digraphs, and zero-one matrices A satisfying A^2=J, (2002), expanded version.
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 31 2011
STATUS
approved