This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A078102 #14 Aug 27 2019 09:51:55
%S A078102 2,27,853,63267,11045757,4547477370,4419979346851,10150938472416408,
%T A078102 55117503183129188479,707887801249881516079368,
%U A078102 21511908182992495395699279579,1547207013442473554135873920560606,263429541331756165013316290711160389207
%N A078102 1/6 of the number of ways of 3-coloring an (n-2) X n grid.
%C A078102 Also the number of 3-colorings of the P_{n-2} X P_n grid graph up to permutation of the colors. - _Andrew Howroyd_, Jun 26 2017
%D A078102 Michael S. Paterson (Warwick), personal communication.
%F A078102 See A078099 for formula.
%F A078102 a(n) = A207997(n-2, n) = A078099(n-2, n)/2. - _Andrew Howroyd_, Jun 26 2017
%t A078102 M[1] = {{1}}; M[m_] := M[m] = {{M[m - 1], Transpose[M[m - 1]]}, {Array[0&, {2^(m - 2), 2^(m - 2)}], M[m - 1]}} // ArrayFlatten;
%t A078102 W[m_] := M[m] + Transpose[M[m]];
%t A078102 T[m_, 1] := 2^(m - 1); T[1, n_] := 2^(n - 1); T[m_, n_] := MatrixPower[ W[m], n - 1] // Flatten // Total;
%t A078102 a[n_] := T[n - 2, n]/2;
%t A078102 Table[a[n], {n, 3, 15}] (* _Jean-François Alcover_, Aug 27 2019 *)
%Y A078102 A diagonal of A078099 and A207997.
%K A078102 nonn
%O A078102 3,1
%A A078102 _N. J. A. Sloane_, Dec 05 2002
%E A078102 a(7)-a(14) from _Alois P. Heinz_, Mar 24 2009
%E A078102 Name clarified and a(15) from _Andrew Howroyd_, Jun 26 2017