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 A004274 #20 Jun 25 2023 20:32:22
%S A004274 0,1,2,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,
%T A004274 47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,
%U A004274 93,95,97,99,101,103,105,107,109,111,113,115,117,119,121,123,125,127,129,131
%N A004274 0, 2 and the odd numbers.
%H A004274 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2, -1).
%F A004274 A004280 UNION {0}. - _R. J. Mathar_, Oct 28 2008
%F A004274 a(n) = 2*n - 3 + floor(2/n), n > 0. - _Wesley Ivan Hurt_, May 23 2013
%F A004274 From _Chai Wah Wu_, Apr 24 2017: (Start)
%F A004274 a(n) = 2*a(n-1) - a(n-2) for n > 4.
%F A004274 G.f.: x*(1 + x^3)/(1 - x)^2. (End)
%t A004274 Join[{0,1,2},Range[3,151,2]] (* _Harvey P. Dale_, Aug 24 2012 *)
%Y A004274 Cf. A004280.
%K A004274 easy,nonn
%O A004274 0,3
%A A004274 _N. J. A. Sloane_