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 A097266 #6 Feb 16 2025 08:32:54
%S A097266 0,1,0,1,2,2,1,2,2,3,4,3,2,5,3,4,7,4,4,6,5,6,6,6,7,9,6,6,11,8,7,12,5,
%T A097266 9,12,9,9,10,12,10,14,11,7,14,11,12,16,10,12,19,12,13,16,14,13,18,14,
%U A097266 12,18,16,17,21,12,16,23,17,20,18,17,18,24,18,13,28,18,19,25,16,19,26,24
%N A097266 Number of primitive Pythagorean quadruples with diagonal 2n+1.
%C A097266 There are no such quadruples with diagonal 2n. - _Michael Somos_, Nov 17 2018
%H A097266 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PythagoreanQuadruple.html">Pythagorean Quadruple.</a>
%t A097266 a[ n_] := With[ {w = 2 n + 1}, Sum[ Boole[x^2 + y^2 + z^2 == w^2 && 1 == GCD[x, y, z, w]], {z, w - 1}, {y, z}, {x, y}]]; (* _Michael Somos_, Nov 17 2018 *)
%o A097266 (PARI) {a(n) = my(w = 2*n+1); sum(z=1, w-1, sum(y=1, z, sum(x=1, y, x^2 + y^2 + z^2 == w^2 && 1 == gcd([x, y, z, w]))))}; /* _Michael Somos_, Nov 17 2018 */
%Y A097266 Cf. A096907-A096909, A097263-A097265.
%K A097266 nonn
%O A097266 0,5
%A A097266 _Ray Chandler_, Aug 16 2004