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 A273264 #15 May 21 2016 22:53:05
%S A273264 2,3,4,5,5,5,5,4,3,3,2,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
%T A273264 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
%U A273264 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
%N A273264 Volume of unit n-ball, rounded to the nearest integer.
%H A273264 Wikipedia, <a href="http://en.wikipedia.org/wiki/Volume_of_an_n-ball">Volume of an n-ball</a>.
%F A273264 a(n) = round((Pi^(n/2)) / (Gamma(1 + n/2))).
%e A273264 The volume of the unit 3-ball (the set of points of distance equal to or less than the radius of the midpoint of the ordinary sphere or 2-sphere) is equal to 4/3*Pi, which is 4.1887902047... (A019699) and when rounded down this is 4, so a(3) = 4.
%t A273264 Table[Round[(Pi^(n/2))/Gamma[1 + n/2]], {n, 120}] (* _Michael De Vlieger_, May 19 2016 *)
%o A273264 (PARI) a(n) = round((Pi^(n/2)) / (gamma(1+n/2)))
%Y A273264 Cf. A019699, A177677, A228272.
%K A273264 nonn,easy
%O A273264 1,1
%A A273264 _Felix Fröhlich_, May 18 2016