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 A169721 #25 Sep 08 2022 08:45:49
%S A169721 1,16,100,484,2116,8836,36100,145924,586756,2353156,9424900,37724164,
%T A169721 150945796,603881476,2415722500,9663283204,38653919236,154617249796,
%U A169721 618472144900,2473894871044,9895592067076,39582393434116,158329624068100,633318596935684
%N A169721 a(n) = (2*(3*2^(n-1)-1))^2.
%C A169721 A subsequence of the squares (A000290).
%H A169721 Vincenzo Librandi, <a href="/A169721/b169721.txt">Table of n, a(n) for n = 0..1000</a>
%H A169721 Alice V. Kleeva, <a href="/A169721/a169721a.jpg">Grid for this sequence</a>
%H A169721 Alice V. Kleeva, <a href="/A169721/a169721b.jpg">Illustration of initial terms</a>
%H A169721 Robert Munafo, <a href="http://www.mrob.com/pub/math/seq-a169720.html">Sequence A169720, and two others by Alice V. Kleeva</a>
%H A169721 Robert Munafo, <a href="/A169720/a169720.pdf">Sequence A169720, and two others by Alice V. Kleeva</a> [Cached copy, in pdf format, included with permission]
%H A169721 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,-14,8).
%F A169721 a(n) = A033484(n)^2.
%F A169721 G.f.: (1+9*x+2*x^2)/(1-7*x+14*x^2-8*x^3). - _Bruno Berselli_, Dec 04 2012
%F A169721 a(n) = 7*a(n-1)-14*a(n-2)+8*a(n-3). - _Vincenzo Librandi_, Dec 04 2012
%t A169721 Table[(2(3*2^(n-1)-1))^2,{n,0,30}] (* _Harvey P. Dale_, Oct 29 2012 *)
%t A169721 CoefficientList[Series[(1+x)/((1-x)*(1-2*x)), {x, 0, 30}], x]^2 (* _Vincenzo Librandi_, Dec 04 2012 *)
%o A169721 (Magma) I:=[1,16,100]; [n le 3 select I[n] else 7*Self(n-1)-14*Self(n-2)+8*Self(n-3): n in [1..30]];// _Vincenzo Librandi_, Dec 04 2012
%Y A169721 Cf. A169720-A169727.
%K A169721 nonn,easy
%O A169721 0,2
%A A169721 Alice V. Kleeva (alice27353(AT)gmail.com), Jan 19 2010