A068254 - OEIS

%I #18 Sep 23 2019 06:27:42

%S 1,21,2403,1500183,5110723191,95013316876491,9639473169171326643,

%T 5336900216006709884938623,16124704040675904181778734982451,

%U 265865038636937159336134567410478299051

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

%H Jean-François Alcover, <a href="/A068254/b068254.txt">Table of n, a(n) for n = 1..16</a>

%t A222444 = Cases[Import["https://oeis.org/A222444/b222444.txt", "Table"], {_, _}][[All, 2]];

%t a[n_] := A222444[[2 n^2 - 2 n + 1]];

%t Table[a[n], {n, 1, 16}] (* _Jean-François Alcover_, Sep 23 2019 *)

%Y Main diagonal of A222444.

%Y Cf. A068239-A068305, A000332, A002417, A027441, A182368, A182406.

%K nonn

%O 1,2

%A _R. H. Hardin_, Feb 24 2002

%E a(9)-a(10) from _Alois P. Heinz_, Apr 27 2012