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 A273368 #17 Nov 08 2018 11:14:48
%S A273368 0,4,16,28,52,72,108,136,184,220,280,324,396,448,532,592,688,756,864,
%T A273368 940,1060,1144,1276,1368,1512,1612,1768,1876,2044,2160,2340,2464,2656,
%U A273368 2788,2992,3132,3348,3496,3724,3880,4120,4284,4536
%N A273368 Numbers k such that 10*k+9 is a perfect square.
%H A273368 G. C. Greubel, <a href="/A273368/b273368.txt">Table of n, a(n) for n = 0..1000</a>
%H A273368 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1, 2, -2, -1, 1).
%F A273368 a(2n) = 10*n^2 + 6*n, n>=0.
%F A273368 a(2n-1) = 10*n^2 - 6*n, n>=1.
%F A273368 G.f.: 4*x*(x^2+3x+1)/((1-x)^3*(1+x)^2).
%F A273368 From _G. C. Greubel_, May 21 2016: (Start)
%F A273368 E.g.f.: (1/2)*((5*x^2 + 9*x)*cosh(x) + (5*x^2 + 11*x -1)*sinh(x)).
%F A273368 a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5). (End)
%F A273368 a(n) = 4*A085787(n). - _R. J. Mathar_, Jun 03 2016
%t A273368 CoefficientList[Series[4*x*(x^2+3x+1)/((1-x)^3*(1+x)^2), {x,0,50}], x] (* or *) LinearRecurrence[{1, 2, -2, -1, 1}, {0, 4, 16, 28, 52}, 50] (* _G. C. Greubel_, May 20 2016 *)
%o A273368 (PARI) is(n)=issquare(10*n+9) \\ _Charles R Greathouse IV_, Jan 31 2017
%Y A273368 Cf. A132356, A273365, A273366, A273367.
%Y A273368 Cf. A033583 (perfect squares ending in 0 in base 10 with final 0 removed).
%K A273368 nonn,easy
%O A273368 0,2
%A A273368 _Nathan Fox_, _Brooke Logan_, and _N. J. A. Sloane_, May 20 2016