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 A213559 #12 Jun 18 2017 02:23:13
%S A213559 1,91,1366,9542,43535,151313,435324,1089804,2452269,5071495,9794290,
%T A213559 17873362,31098587,51953981,83802680,131102232,199652505,296878515,
%U A213559 432150478,617143390,866238439,1196968553,1630510388,2192225060
%N A213559 Principal diagonal of the convolution array A213558.
%H A213559 Clark Kimberling, <a href="/A213559/b213559.txt">Table of n, a(n) for n = 1..1000</a>
%H A213559 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (8,-28,56,-70,56,-28,8,-1).
%F A213559 a(n) = (16/35)*n^7 + (1/2)*n^6 + (1/15)*n^3 - (1/42)*n.
%F A213559 a(n) = 8*a(n-1) - 28*a(n-2) + 56*a(n-3) - 70*a(n-4) + 56*a(n-5) - 28*a(n-6) + 8*a(n-7) - a(n-8).
%F A213559 G.f.: x*(1 + 83*x + 666*x^2 + 1106*x^3 + 421*x^4 + 27*x^5)/(1 - x)^8
%t A213559 (See A213558.)
%t A213559 LinearRecurrence[{8,-28,56,-70,56,-28,8,-1},{1,91,1366,9542,43535,151313,435324,1089804},40] (* _Harvey P. Dale_, Oct 09 2016 *)
%Y A213559 Cf. A213558, A213500.
%K A213559 nonn,easy
%O A213559 1,2
%A A213559 _Clark Kimberling_, Jun 17 2012