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 A259163 #11 Aug 16 2015 12:04:01
%S A259163 18,189,37727235,393298308,78448579122960,817809556618215,
%T A259163 163122994382238923193,1700522115268371779430,
%U A259163 339191755844562643229618814,3536001066647854270462804353,705302447816298343956844397692383,7352626249945315029422809413582264
%N A259163 Positive heptagonal numbers (A000566) that are triangular numbers (A000217) divided by 2.
%C A259163 Intersection of A000566 and A074378 (even triangular numbers divided by 2). - _Michel Marcus_, Jun 20 2015
%H A259163 Colin Barker, <a href="/A259163/b259163.txt">Table of n, a(n) for n = 1..317</a>
%H A259163 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,2079362,-2079362,-1,1).
%F A259163 G.f.: -9*x*(2*x^4+19*x^3+33170*x^2+19*x+2) / ((x-1)*(x^2-1442*x+1)*(x^2+1442*x+1)).
%e A259163 18 is in the sequence because 18 is the 3rd heptagonal number, and 2*18 is the 8th triangular number.
%t A259163 LinearRecurrence[{1, 2079362, -2079362, -1, 1}, {18, 189, 37727235, 393298308, 78448579122960}, 20] (* _Vincenzo Librandi_, Jun 20 2015 *)
%o A259163 (PARI) Vec(-9*x*(2*x^4+19*x^3+33170*x^2+19*x+2)/((x-1)*(x^2-1442*x+1)*(x^2+1442*x+1)) + O(x^20))
%Y A259163 Cf. A000217, A000566, A074378, A259156-A259162, A259164-A259167.
%K A259163 nonn,easy
%O A259163 1,1
%A A259163 _Colin Barker_, Jun 19 2015