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 A211416 #9 Jan 22 2020 09:58:49
%S A211416 0,14,22,38,54,70,86,102,134,150,166,182,214,230,246,278,310,326,342,
%T A211416 358,390,422,438,454,518,534,550,566,598,614,646,662,694,726,742,774,
%U A211416 806,822,838,870,934,950,982,998,1030,1062,1078,1094,1158,1174
%N A211416 Number of self-inverse 2 X 2 matrices with all terms in {-n,...,0,...,n}.
%e A211416 The 14 matrices counted by a(1) are as follows:
%e A211416 ...
%e A211416 1 0...-1 0...-1 -1...-1 0...-1 0...-1 0...-1 1
%e A211416 0 1... 0 -1...0 1...-1 1....0 1 ...1 1... 0 1
%e A211416 ...
%e A211416 0 -1...0 1...1 -1... 1 0....1 0....1 0....1 1
%e A211416 -1 0...1 0...0 -1...-1 -1...0 -1...1 -1...0 1
%t A211416 t[n_] := t[n] = Flatten[Table[w^2 + x*y - 1, {w, -n, n}, {x, -n, n}, {y, -n, n}]]
%t A211416 c[n_] := Count[t[n], 0]
%t A211416 t = Table[c[n], {n, 0, 20}] (* A211415 *)
%t A211416 t + 2 (* A211416 *)
%t A211416 (t + 2)/2 (* integers *)
%t A211416 t/4 (* integers *)
%t A211416 (t/4 - 1)/4 (* integers for n>1 *)
%Y A211416 Cf. A211415.
%K A211416 nonn
%O A211416 0,2
%A A211416 _Clark Kimberling_, Apr 09 2012
%E A211416 Offset corrected by _Pontus von Brömssen_, Jan 22 2020