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 A271994 #18 Sep 24 2022 12:38:54
%S A271994 8,16,34,52,84,116,166,216,288,360,458,556,684,812,974,1136,1336,1536,
%T A271994 1778,2020,2308,2596,2934,3272,3664,4056,4506,4956,5468,5980,6558,
%U A271994 7136,7784,8432,9154,9876,10676,11476,12358,13240,14208,15176,16234,17292,18444
%N A271994 The chalcogen sequence (a(n) = A018227(n)-2).
%C A271994 Terms up to 116 are the atomic numbers of the elements of group 16 in the periodic table. Those elements are also known as chalcogens.
%H A271994 Colin Barker, <a href="/A271994/b271994.txt">Table of n, a(n) for n = 2..1000</a>
%H A271994 Wikipedia, <a href="https://en.wikipedia.org/wiki/Chalcogen">Chalcogen</a>
%H A271994 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-4,1,2,-1).
%F A271994 From _Colin Barker_, May 29 2016: (Start)
%F A271994 a(n) = 2*a(n-1)+a(n-2)-4*a(n-3)+a(n-4)+2*a(n-5)-a(n-6) for n>7.
%F A271994 G.f.: 2*x^2*(4-3*x^2+x^4) / ((1-x)^4*(1+x)^2).
%F A271994 (End)
%F A271994 a(n) = (2*n^3 + 12*n^2 + 25*n + (-1)^n*3*(n + 2) - 30)/12. - _Ilya Gutkovskiy_, May 29 2016
%t A271994 Table[(2 n^3 + 12 n^2 + 25 n + (-1)^n 3 (n + 2) - 30)/12, {n, 2, 43}] (* or *)
%t A271994 Drop[#, 2] &@ CoefficientList[Series[2 x^2 (4 - 3 x^2 + x^4)/((1 - x)^4 (1 + x)^2), {x, 0, 43}], x] (* _Michael De Vlieger_, May 29 2016 *)
%t A271994 LinearRecurrence[{2,1,-4,1,2,-1},{8,16,34,52,84,116},50] (* _Harvey P. Dale_, Sep 24 2022 *)
%o A271994 (PARI) Vec(2*x^2*(4-3*x^2+x^4)/((1-x)^4*(1+x)^2) + O(x^50)) \\ _Colin Barker_, May 29 2016
%K A271994 nonn,easy
%O A271994 2,1
%A A271994 _Natan Arie Consigli_, May 28 2016