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A068254 1/4 the number of colorings of an n X n square array with 4 colors.

%I A068254 #18 Sep 23 2019 06:27:42
%S A068254 1,21,2403,1500183,5110723191,95013316876491,9639473169171326643,
%T A068254 5336900216006709884938623,16124704040675904181778734982451,
%U A068254 265865038636937159336134567410478299051
%N A068254 1/4 the number of colorings of an n X n square array with 4 colors.
%H A068254 Jean-François Alcover, <a href="/A068254/b068254.txt">Table of n, a(n) for n = 1..16</a>
%t A068254 A222444 = Cases[Import["https://oeis.org/A222444/b222444.txt", "Table"], {_, _}][[All, 2]];
%t A068254 a[n_] := A222444[[2 n^2 - 2 n + 1]];
%t A068254 Table[a[n], {n, 1, 16}] (* _Jean-François Alcover_, Sep 23 2019 *)
%Y A068254 Main diagonal of A222444.
%Y A068254 Cf. A068239-A068305, A000332, A002417, A027441, A182368, A182406.
%K A068254 nonn
%O A068254 1,2
%A A068254 _R. H. Hardin_, Feb 24 2002
%E A068254 a(9)-a(10) from _Alois P. Heinz_, Apr 27 2012