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 A011918 #28 Mar 05 2016 05:25:14
%S A011918 5,76,1065,14840,206701,2878980,40099025,558507376,7779004245,
%T A011918 108347552060,1509086724601,21018866592360,292755045568445,
%U A011918 4077551771365876,56792969753553825,791024024778387680,11017543377143873701,153454583255235844140,2137346622196157944265
%N A011918 a(n) = A011916(n) + A011922(n) - 1.
%C A011918 Also integers n such that n^2+(n+1)^2 is equal to the sum of two consecutive octagonal numbers. - _Colin Barker_, Dec 20 2014
%D A011918 Mario Velucchi, "Seeing couples", Recreational and Educational Computing, to appear 1997. [apparently never materialized, _Joerg Arndt_, Aug 14 2013]
%H A011918 Vincenzo Librandi, <a href="/A011918/b011918.txt">Table of n, a(n) for n = 1..200</a>
%H A011918 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (15,-15,1).
%F A011918 a(n) = +15*a(n-1) -15*a(n-2) +a(n-3). G.f.: -x*(5+x)/ ((x-1) * (x^2-14*x+1)). - _R. J. Mathar_, Apr 15 2010
%F A011918 a(n) = (A007655(n+2) - 3*A007655(n+1) - 1)/2. - _Ralf Stephan_, Aug 13 2013
%F A011918 a(n) = (-6-(7-4*sqrt(3))^n*(-3+sqrt(3))+(3+sqrt(3))*(7+4*sqrt(3))^n)/12. - _Colin Barker_, Mar 05 2016
%t A011918 CoefficientList[Series[-(5 + x) / ((x - 1) (x^2 - 14 x + 1)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Aug 13 2013 *)
%o A011918 (PARI) Vec(-x*(5+x)/((x-1)*(x^2-14*x+1)) + O(x^100)) \\ _Colin Barker_, Dec 20 2014
%Y A011918 Cf. A011916.
%K A011918 nonn,easy
%O A011918 1,1
%A A011918 Mario Velucchi (mathchess(AT)velucchi.it)
%E A011918 More terms from _R. J. Mathar_, Apr 15 2010