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 A213842 #13 Jun 17 2017 02:59:44 %S A213842 1,24,101,264,545,976,1589,2416,3489,4840,6501,8504,10881,13664,16885, %T A213842 20576,24769,29496,34789,40680,47201,54384,62261,70864,80225,90376, %U A213842 101349,113176,125889,139520,154101,169664 %N A213842 Principal diagonal of the convolution array A213841. %H A213842 Clark Kimberling, <a href="/A213842/b213842.txt">Table of n, a(n) for n = 1..1000</a> %H A213842 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1). %F A213842 a(n) = (2*n - 15*n^2 + 16*n^3)/3. %F A213842 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4). %F A213842 G.f.: f(x)/g(x), where f(x) = x*(1 + 20*x + 11*x^2) and g(x) = (1-x)^4. %t A213842 (See A213841.) %Y A213842 Cf. A213841. %K A213842 nonn,easy %O A213842 1,2 %A A213842 _Clark Kimberling_, Jul 05 2012