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 A098148 #16 Dec 14 2018 09:20:11
%S A098148 0,0,52,22196,21005094
%N A098148 Number of real (0,1) n X n matrices such that some eigenvalues are strictly complex.
%H A098148 <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>
%e A098148 The 3 X 3 matrix ((0,1,0),(0,0,1),(1,1,1)) has real eigenvalue 1.83929 and the complex pair -0.41964+-0.60629*i. There are 12 (0,1) 3 X 3 matrices with these eigenvalues. There are 6 groups of 6 matrices having eigenvalues (1.3472,-0.66236+-0.56228*i), (1.46557,-0.23279+-0.79255*i),..., (2.32472,0.33764+-0.56228*i). Two matrices (e.g. ((0,0,1),(1,0,0),(0,1,0)) ) have eigenvalues (1,-0.5+-0.5*sqrt(3)*i). Two matrices (e.g. ((1,1,0),(0,1,1),(1,0,1)) ) have eigenvalues (2,0.5+-0.5*sqrt(3)*i). Total: 12+6*6+2+2=52=a(3).
%t A098148 a[n_] := Module[{M, iter, cnt=0}, M = Table[a[i, j], {i, 1, n}, {j, 1, n}]; iter = Thread[{Flatten[M], 0, 1}]; Do[If[AnyTrue[Eigenvalues[M], Im[#] != 0&], cnt++], Evaluate[Sequence @@ iter]]; cnt];
%t A098148 Do[Print[n, " ", a[n]], {n, 1, 4}] (* _Jean-François Alcover_, Dec 09 2018 *)
%Y A098148 Cf. other counts for (0, 1) matrices: A003024 (positive eigenvalues), A055165 (nonsingular), A085656 (positive definite), A086510 (nonnegative eigenvalues).
%K A098148 more,nonn
%O A098148 1,3
%A A098148 _Hugo Pfoertner_, Sep 07 2004
%E A098148 a(5) corrected by _Hugo Pfoertner_, Sep 26 2017