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 A005818 #32 Feb 15 2025 02:12:25
%S A005818 3,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,
%T A005818 53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,93,95,97,
%U A005818 99,101,103,105,107,109,111,113,115,117,119,121,123,125,127,129,131
%N A005818 Numbers n that are primitive solutions to n^2 = a^2 + b^2 + c^2 (a,b,c > 0).
%C A005818 These are the odd numbers excluding 1 and 5. Every term in A005767 is n*2^k for some k.
%H A005818 T. D. Noe, <a href="/A005818/b005818.txt">Table of n, a(n) for n = 1..1000</a>
%H A005818 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A005818 G.f.: x*(-2*x^2 + x + 3)/(x - 1)^2. - _Chai Wah Wu_, Sep 14 2018
%F A005818 E.g.f.: (exp(x) - 1)*(3 + 2*x). - _Stefano Spezia_, Feb 19 2023
%t A005818 Join[{3}, Range[7, 200, 2]] (* _Paolo Xausa_, Feb 14 2025 *)
%o A005818 (Python)
%o A005818 def A005818(n): return (n<<1)+3 if n>1 else 3 # _Chai Wah Wu_, Feb 14 2025
%Y A005818 Cf. A005767.
%K A005818 nonn,easy
%O A005818 1,1
%A A005818 _N. J. A. Sloane_, RALPH PETERSON (ralphp(AT)LIBRARY.NRL.NAVY.MIL)
%E A005818 Name corrected by _T. D. Noe_, Nov 12 2010