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 A259159 #10 Aug 16 2015 12:04:01
%S A259159 9,938961,97353360225,10093791093915321,1046544448101974957529,
%T A259159 108507821458015176452612289,11250307943363385076857772396401,
%U A259159 1166454428075294670080752381151042025,120940328000452394039949183305644566845481
%N A259159 Positive squares (A000290) that are heptagonal numbers (A000566) divided by 2.
%H A259159 Colin Barker, <a href="/A259159/b259159.txt">Table of n, a(n) for n = 1..200</a>
%H A259159 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (103683,-103683,1).
%F A259159 G.f.: -9*x*(x^2+646*x+1) / ((x-1)*(x^2-103682*x+1)).
%e A259159 9 is in the sequence because 9 is the 3rd square, and 2*9 is the 3rd heptagonal number.
%t A259159 LinearRecurrence[{103683, -103683, 1},{9, 938961, 97353360225}, 20] (* _Vincenzo Librandi_, Jun 20 2015 *)
%o A259159 (PARI) Vec(-9*x*(x^2+646*x+1)/((x-1)*(x^2-103682*x+1)) + O(x^20))
%Y A259159 Cf. A000290, A000566, A259156-A259158, A259160-A259167.
%K A259159 nonn,easy
%O A259159 1,1
%A A259159 _Colin Barker_, Jun 19 2015