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 A259079 #17 Dec 25 2019 23:10:00
%S A259079 280,373212840,497012764340408,661878856450449219400,
%T A259079 881433339438556519000044120,1173817118196415977287174306335208,
%U A259079 1563188689740940473437573487667885475320,2081720262768492984525248323578863263574296200
%N A259079 Octagonal numbers (A000567) that are other octagonal numbers divided by 2.
%C A259079 Intersection of A000567 and A033579 (even octagonal numbers divided by 2). - _Michel Marcus_, Jun 20 2015
%H A259079 Colin Barker, <a href="/A259079/b259079.txt">Table of n, a(n) for n = 1..163</a>
%H A259079 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1331715,-1331715,1).
%F A259079 G.f.: -8*x*(x^2+41580*x+35) / ((x-1)*(x^2-1331714*x+1)).
%e A259079 280 is in the sequence because 280 is the 10th octagonal number, and 2*280 is the 14th octagonal number.
%t A259079 LinearRecurrence[{1331715,-1331715,1},{280,373212840,497012764340408},20] (* _Harvey P. Dale_, Dec 04 2015 *)
%o A259079 (PARI) Vec(-8*x*(x^2+41580*x+35)/((x-1)*(x^2-1331714*x+1)) + O(x^20))
%Y A259079 Cf. A000567, A075528, A107736, A259078.
%K A259079 nonn,easy
%O A259079 1,1
%A A259079 _Colin Barker_, Jun 18 2015