A060767 Erroneous version of A057981.
1, 33, 78705, 15099201
Offset: 1
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a(1) = 2: [1], [ -1]. a(2) = 48: There are 8 choices for the first column, u (say) and then the 2nd column can be anything except 0, u, -u, so 6 choices, giving a total of 8*6 = 48.
(* A brute force solution up to n = 4 *) a[n_] := a[n] = (m = Array[x, {n, n}]; cnt = 0; iter = {#, -1, 1}& /@ Flatten[m]; Do[ If[ Det[m] != 0, cnt++], Evaluate[ Sequence @@ iter]]; cnt); Table[ Print[a[n]]; a[n], {n, 1, 4}] (* Jean-François Alcover, Oct 11 2012 *)
a[n_] := Sum[Boole[Permanent[m] == 0], {m, Tuples[{-1, 0, 1}, {n, n}]}];
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