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 A294178 #53 Nov 13 2023 08:44:20
%S A294178 1,3,3,9,5,15,7,21,9,27,11,33,13,39,15,45,17,51,19,57,21,63,23,69,25,
%T A294178 75,27,81,29,87,31,93,33,99,35,105,37,111,39,117,41,123,43,129,45,135,
%U A294178 47,141,49,147,51,153
%N A294178 a(2n) = 2*n + 1, a(2n+1) = 6*n + 3.
%H A294178 Colin Barker, <a href="/A294178/b294178.txt">Table of n, a(n) for n = 0..1000</a>
%H A294178 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,2,0,-1).
%F A294178 a(n) = 2*a(n-2) - a(n-4).
%F A294178 a(n) = A289296(n+1) - A289296(n).
%F A294178 G.f.: (1 + 3*x)*(1 + x^2) / ((1 - x)^2*(1 + x)^2). - _Colin Barker_, Jun 29 2018
%t A294178 LinearRecurrence[{0,2,0,-1},{1,3,3,9},100] (* _Paolo Xausa_, Nov 13 2023 *)
%o A294178 (PARI) Vec((1 + 3*x)*(1 + x^2) / ((1 - x)^2*(1 + x)^2) + O(x^40)) \\ _Colin Barker_, Jun 29 2018
%Y A294178 Cf. A029578, A289296.
%K A294178 nonn,easy
%O A294178 0,2
%A A294178 _Paul Curtz_, Jun 28 2018