OFFSET
1,2
LINKS
MATHEMATICA
a[n_] := Sum[Boole[Permanent[m] == 0], {m, Tuples[{-1, 0, 1}, {n, n}]}];
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Hongyang Cao, Dec 02 2019
EXTENSIONS
a(6) from Peter J. Taylor, Dec 16 2019
STATUS
approved