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 A055549 #24 Aug 09 2025 07:34:41
%S A055549 3,33,939,75041,15901363,10833591489
%N A055549 Number of normal n X n (-1,0,1)-matrices.
%D A055549 W. H. Press et al., Numerical Recipes, Cambridge, 1986; Chapter 11.
%H A055549 Georg Muntingh, <a href="/A055549/a055549.txt">Sage code for recursively computing higher entries</a>
%H A055549 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/NormalMatrix.html">Normal Matrix.</a>
%t A055549 normalQ[a_] := Block[{b=Transpose[a]}, a.b === b.a]; cnt[n_]:= Block[{c=0,q=n^2}, Do[If[normalQ@Partition[IntegerDigits[t-1,3,q]-1, n], c++ ],{t,3^q}]; c]; Array[cnt,4] (* _Giovanni Resta_, Apr 03 2006 *)
%Y A055549 Cf. A055547, A055548.
%K A055549 nonn,more,hard
%O A055549 1,1
%A A055549 _Eric W. Weisstein_
%E A055549 a(4) from _Giovanni Resta_, Apr 03 2006
%E A055549 a(5) from _Georg Muntingh_, Feb 03 2014
%E A055549 a(6) from _Bert Dobbelaere_, Sep 20 2020