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 A195015 #28 Feb 09 2024 07:44:36
%S A195015 0,2,12,24,44,66,96,128,168,210,260,312,372,434,504,576,656,738,828,
%T A195015 920,1020,1122,1232,1344,1464,1586,1716,1848,1988,2130,2280,2432,2592,
%U A195015 2754,2924,3096,3276,3458,3648,3840,4040,4242,4452,4664,4884
%N A195015 Main axis of the square spiral whose edges have length A195013 and whose vertices are the numbers A195014.
%C A195015 Sequence found by reading the line from 0, in the direction 0, 2, ..., and the same line from 0, in the direction 0, 12, ..., in the square spiral mentioned above. Axis perpendicular to A195016 in the same spiral.
%C A195015 Also four times A005475 and positives A152965 interleaved.
%H A195015 Vincenzo Librandi, <a href="/A195015/b195015.txt">Table of n, a(n) for n = 0..10000</a>
%H A195015 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A195015 From _Bruno Berselli_, Oct 14 2011: (Start)
%F A195015 G.f.: 2*x*(1+4*x)/((1+x)*(1-x)^3).
%F A195015 a(n) = (2*n*(5*n+2) + 3*(-1)^n-3)/4.
%F A195015 a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4).
%F A195015 a(n) + a(n-1) = A135706(n). (End)
%t A195015 LinearRecurrence[{2, 0, -2, 1}, {0, 2, 12, 24}, 50] (* _Paolo Xausa_, Feb 09 2024 *)
%o A195015 (Magma) [(2*n*(5*n+2)+3*(-1)^n-3)/4: n in [0..50]]; // _Vincenzo Librandi_, Oct 28 2011
%Y A195015 Cf. A000566, A005475, A005476, A028895, A033571, A152965, A153126, A195013, A195014, A195016.
%K A195015 nonn,easy
%O A195015 0,2
%A A195015 _Omar E. Pol_, Sep 26 2011