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 A213769 #17 Feb 19 2024 03:02:12
%S A213769 1,8,26,63,136,272,521,968,1762,3159,5600,9840,17169,29784,51418,
%T A213769 88399,151432,258592,440345,747960,1267586,2143783,3618816,6098208,
%U A213769 10260001,17236712,28918106,48454623,81093832,135569264,226404905
%N A213769 Principal diagonal of the convolution array A213768.
%H A213769 Clark Kimberling, <a href="/A213769/b213769.txt">Table of n, a(n) for n = 1..1000</a>
%H A213769 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (4,-4,-2,4,0,-1).
%F A213769 a(n) = 4*a(n-1) - 4*a(n-2) - 2*a(n-3) + 4*a(n-4) - a(n-6).
%F A213769 G.f.: f(x)/g(x), where f(x) = x*(1 + 4*x - 2*x^2 - 7*x^3) and g(x) = (1 - 2*x + x^3 )^2.
%t A213769 (See A213768.)
%t A213769 LinearRecurrence[{4,-4,-2,4,0,-1},{1,8,26,63,136,272},40] (* _Harvey P. Dale_, Jan 08 2015 *)
%Y A213769 Cf. A213768, A213500.
%K A213769 nonn,easy
%O A213769 1,2
%A A213769 _Clark Kimberling_, Jun 21 2012