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 A213848 #12 Jun 17 2017 02:59:45 %S A213848 3,36,131,320,635,1108,1771,2656,3795,5220,6963,9056,11531,14420, %T A213848 17755,21568,25891,30756,36195,42240,48923,56276,64331,73120,82675, %U A213848 93028,104211,116256,129195,143060,157883,173696 %N A213848 Principal diagonal of the convolution array A213847. %H A213848 Clark Kimberling, <a href="/A213848/b213848.txt">Table of n, a(n) for n = 1..1000</a> %H A213848 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1). %F A213848 a(n) = (-4*n - 3*n^2 + 16*n^3)/3. %F A213848 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4). %F A213848 G.f.: f(x)/g(x), where f(x) = x*(3 + 24*x + 5*x^2) and g(x) = (1-x)^4. %t A213848 (See A213841.) %Y A213848 Cf. A213841. %K A213848 nonn,easy %O A213848 1,1 %A A213848 _Clark Kimberling_, Jul 05 2012