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 A259164 #11 Aug 16 2015 12:04:01
%S A259164 18,1877922,194706720450,20187582187830642,2093088896203949915058,
%T A259164 217015642916030352905224578,22500615886726770153715544792802,
%U A259164 2332908856150589340161504762302084050,241880656000904788079898366611289133690962
%N A259164 Positive heptagonal numbers (A000566) that are squares (A000290) divided by 2.
%C A259164 Intersection of A000566 and A001105 (even squares divided by 2). - _Michel Marcus_, Jun 20 2015
%H A259164 Colin Barker, <a href="/A259164/b259164.txt">Table of n, a(n) for n = 1..200</a>
%H A259164 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (103683,-103683,1).
%F A259164 G.f.: -18*x*(x^2+646*x+1) / ((x-1)*(x^2-103682*x+1)).
%e A259164 18 is in the sequence because 18 is the 3rd heptagonal number, and 2*18 is the 6th square.
%t A259164 LinearRecurrence[{103683, -103683, 1}, {18, 1877922, 194706720450}, 20] (* _Vincenzo Librandi_, Jun 20 2015 *)
%o A259164 (PARI) Vec(-18*x*(x^2+646*x+1)/((x-1)*(x^2-103682*x+1)) + O(x^20))
%Y A259164 Cf. A000290, A000566, A001105, A259156-A259163, A259165-A259167.
%K A259164 nonn,easy
%O A259164 1,1
%A A259164 _Colin Barker_, Jun 19 2015