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 A016821 #18 Apr 21 2023 05:46:24
%S A016821 1,1953125,387420489,10604499373,118587876497,794280046581,
%T A016821 3814697265625,14507145975869,46411484401953,129961739795077,
%U A016821 327381934393961,756680642578125,1628413597910449,3299763591802133,6351461955384057,11694146092834141,20711912837890625,35452087835576229
%N A016821 a(n) = (4n+1)^9.
%H A016821 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (10,-45,120,-210,252,-210,120,-45,10,-1).
%F A016821 From _Amiram Eldar_, Apr 21 2023: (Start)
%F A016821 a(n) = A016813(n)^9.
%F A016821 Sum_{n>=0} 1/a(n) = 277*Pi^9/16515072 + 511*zeta(9)/1024. (End)
%t A016821 Table[(4n+1)^9,{n,0,100}] (* _Mohammad K. Azarian_, Jun 20 2016 *)
%t A016821 LinearRecurrence[{10,-45,120,-210,252,-210,120,-45,10,-1},{1,1953125,387420489,10604499373,118587876497,794280046581,3814697265625,14507145975869,46411484401953,129961739795077},20] (* _Harvey P. Dale_, Sep 24 2022 *)
%Y A016821 Cf. A013667, A016813.
%K A016821 nonn,easy
%O A016821 0,2
%A A016821 _N. J. A. Sloane_