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 A227867 #23 May 06 2024 01:43:44
%S A227867 1,8,14,32,32,112,58,32,110,256,134,448,184,464,448,32,308,880,382,
%T A227867 1024,812,1072,554,448,752,1472,974,1856,872,3584,994,32,1876,2464,
%U A227867 1856,3520,1408,3056,2576,1024,1724,6496,1894,4288,3520,4432,2258,448,2746,6016,4312,5888
%N A227867 Number of Lipschitz quaternions X such that X^2 == 1 (mod n).
%C A227867 A quaternion q = a + bi + cj + dk is congruent to 1 (mod n) iff a == 1 (mod n) and b == c == d == 0 (mod n).
%H A227867 Wikipedia, <a href="http://en.wikipedia.org/wiki/Hurwitz_quaternion">Hurwitz quaternion</a>.
%t A227867 cuaternios[n_] := Flatten[Table[{{a, -b, d, -c}, {b, a, -c, -d}, {-d, c, a, -b}, {c, d, b, a}}, {a, n}, {b, n}, {c, n}, {d, n}], 3]; invo[n_] := invo[n] = Length@Select[cuaternios[n], Mod[#.# - IdentityMatrix[4],n] == 0*# &]; Table[invo[n], {n, 1, 25}]
%Y A227867 Cf. A227477, A227499, A227628.
%K A227867 nonn,mult
%O A227867 1,2
%A A227867 _José María Grau Ribas_, Nov 02 2013
%E A227867 More terms from _Amiram Eldar_, May 06 2024