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 A213749 #15 Oct 30 2017 12:41:07
%S A213749 1,9,46,180,603,1827,5164,13878,35905,90189,221274,532584,1261687,
%T A213749 2949255,6815896,15597738,35389629,79691985,178258150,396361980,
%U A213749 876609811,1929380139,4227858756,9227469150,20065550713,43486544277,93952410034,202400334288
%N A213749 Antidiagonal sums of the convolution array A213747.
%H A213749 Clark Kimberling, <a href="/A213749/b213749.txt">Table of n, a(n) for n = 1..500</a>
%H A213749 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (9,-33,63,-66,36,-8).
%F A213749 a(n) = 9*a(n-1) - 33*a(n-2) + 63*a(n-3) - 66*a(n-4) + 36*a(n-5) - 8*a(n-6).
%F A213749 G.f.: x*(1 - 2*x^2) / ((1 - x)^3*(1 - 2*x)^3).
%F A213749 a(n) = (1/2)*((1+n)*(4-2^(2+n) + n + 2^(1+n)*n)). - _Colin Barker_, Oct 30 2017
%t A213749 (See A213747.)
%t A213749 LinearRecurrence[{9,-33,63,-66,36,-8},{1,9,46,180,603,1827},30] (* _Harvey P. Dale_, May 16 2013 *)
%o A213749 (PARI) Vec(x*(1 - 2*x^2) / ((1 - x)^3*(1 - 2*x)^3) + O(x^30)) \\ _Colin Barker_, Oct 30 2017
%Y A213749 Cf. A213747, A213500.
%K A213749 nonn,easy
%O A213749 1,2
%A A213749 _Clark Kimberling_, Jun 19 2012