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 A286721 #14 Dec 19 2017 02:15:46
%S A286721 1,12,159,2485,45474,959070,22963996,616224492,18331744896,
%T A286721 599061555136,21339235262784,823098817664448,34183157124707200,
%U A286721 1520908498941532800,72182781516370886400,3640264913563748243200,194408478299496756556800,10961007293837647131724800
%N A286721 Column k=2 of the triangle A286718; Sheffer ((1 - 3*x)^(-1/3), (-1/3)*log(1 - 3*x)).
%C A286721 a(n) is, for n >= 1, the total volume of the binomial(n+2, n) rectangular polytopes (hyper-cuboids) built from n orthogonal vectors with lengths of the sides from the set {1 + 3*j | j=0..n+1}. See the formula a(n) = sigma[3,1]^{(n+2)}_n and an example below.
%F A286721 a(n) = A286718(n+2, 2), n >= 0.
%F A286721 E.g.f.: (d^2/dx^2)((1 - 3*x)^(-1/3)*((-1/3)*log(1 - 3*x))^2/2!) = (2*(log(1-3*x))^2 - 15*log(1-3*x) + 9)/(3^2*(1-3*x)^(7/3)).
%F A286721 a(n) = sigma[3,1]^{(n+2)}_n, n >= 0, with the elementary symmetric function sigma[3,1]^{n+2}_n of degree n of the n+2 numbers 1, 4, 7, ..., (1 + 3*(n+1)).
%e A286721 a(2) = 159 because sigma[3,1]^{(4)}_2 = 1*(4 + 7 + 10) + 4*(7 + 10) + 7*10 = 159. There are six rectangles (2D rectangular polytopes) built from two orthogonal vectors of different lengths from the set of {1,4,7,10} of total area 159.
%Y A286721 Cf. A007559 (k=0), A024216 (k=1), A286718.
%K A286721 nonn,easy
%O A286721 0,2
%A A286721 _Wolfdieter Lang_, May 29 2017