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 A173814 #4 Jun 02 2025 02:42:18
%S A173814 1,1,-4,1,1,-16,30,-16,1,1,-64,676,-2752,4678,-2752,676,-64,1,1,-256,
%T A173814 13560,-316160,3830300,-25002240,87841480,-180202240,227671110,
%U A173814 -180202240,87841480,-25002240,3830300,-316160,13560,-256,1,1,-1024
%N A173814 Coefficients of Hadamard Cartan G_2 self-similar 2^n matrices:M={{2, -1}, {-3, 2}}.
%C A173814 Row sums are:
%C A173814 {1, -2, 0, 400, 0, 231040000000000, 0,...}.
%F A173814 M(2)={{2, -1}, {-3, 2}};
%F A173814 M(4)={{4, -2, -2, 1}, {-6, 4, 3, -2}, {-6, 3, 4, -2}, {9, -6, -6, 4}},etc.
%e A173814 {1},
%e A173814 {1, -4, 1},
%e A173814 {1, -16, 30, -16, 1},
%e A173814 {1, -64, 676, -2752, 4678, -2752, 676, -64, 1},
%e A173814 {1, -256, 13560, -316160, 3830300, -25002240, 87841480, -180202240, 227671110, -180202240, 87841480, -25002240, 3830300, -316160, 13560, -256, 1},
%e A173814 {1, -1024, 255376, -30325760, 2060069240, -86239093760, 2306160223920, -40571580718080, 489632650203420, -4209374685189120, 26512089196724880, -124638699726597120, 442120325884773960, -1188638208146519040, 2420933452415430960, -3721572797083978752, 4298314898249481798, -3721572797083978752, 2420933452415430960, -1188638208146519040, 442120325884773960, -124638699726597120, 26512089196724880, -4209374685189120, 489632650203420, -40571580718080, 2306160223920, -86239093760, 2060069240, -30325760, 255376, -1024, 1}, ...
%t A173814 MatrixJoinH[A_, B_] := Transpose[Join[Transpose[A], Transpose[B]]]
%t A173814 KroneckerProduct[M_, N_] := Module[{M1, N1, LM, LN, N2},
%t A173814 M1 = M;
%t A173814 N1 = N;
%t A173814 LM = Length[M1];
%t A173814 LN = Length[N1];
%t A173814 Do[M1[[i, j]] = M1[[i, j]]N1, {i, 1, LM}, {j, 1, LM}];
%t A173814 Do[M1[[i, 1]] = MatrixJoinH[M1[[i, 1]], M1[[i, j]]], {j, 2, LM}, {i, 1, LM}];
%t A173814 N2 = {};
%t A173814 Do[AppendTo[N2, M1[[i, 1]]], {i, 1, LM}];
%t A173814 N2 = Flatten[N2];
%t A173814 Partition[N2, LM*LN, LM*LN]]
%t A173814 HadamardMatrix[2] := {{2, -1}, {-3, 2}}
%t A173814 HadamardMatrix[n_] := Module[{m},
%t A173814 m = {{2, -1}, {-3, 2}};
%t A173814 KroneckerProduct[m, HadamardMatrix[n/2]]]
%t A173814 Table[HadamardMatrix[2^n], {n, 1, 4}]
%t A173814 Join[{{1}}, Table[CoefficientList[CharacteristicPolynomial[ HadamardMatrix[2^n], x], x], {n, 1, 6}]]
%t A173814 Flatten[%]
%Y A173814 Cf. A136674, A158800
%K A173814 sign,tabl,uned
%O A173814 0,3
%A A173814 _Roger L. Bagula_, Feb 25 2010