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 A117798 #12 Mar 22 2021 05:47:41
%S A117798 0,20,820,1200,3440,4180,7860,8960,14080,15540,22100,23920,31920,
%T A117798 34100,43540,46080,56960,59860,72180,75440,89200,92820,108020,112000,
%U A117798 128640,132980,151060,155760,175280,180340,201300,206720,229120,234900,258740
%N A117798 Icosagonal numbers divisible by 20.
%C A117798 Intersection of A008602 and A051872. - _Michel Marcus_, Feb 27 2014
%H A117798 Daniel Starodubtsev, <a href="/A117798/b117798.txt">Table of n, a(n) for n = 1..10000</a>
%t A117798 Select[Table[PolygonalNumber[20, n], {n, 0, 200}], Divisible[#, 20] &] (* _Amiram Eldar_, Mar 22 2021 *)
%o A117798 (PARI) isok(n) = ispolygonal(n, 20) && !(n % 20); \\ _Michel Marcus_, Feb 27 2014
%Y A117798 Cf. A008602, A051872.
%K A117798 easy,nonn
%O A117798 1,2
%A A117798 Luc Stevens (lms022(AT)yahoo.com), Apr 29 2006