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 A140821 #10 Mar 23 2025 13:48:32
%S A140821 2,2,4,2,4,6,6,6,6,8,8,12,8,8,10,10,20,20,10,10,12,12,60,60,60,12,12,
%T A140821 14,14,42,70,70,42,14,14,16,16,112,112,280,112,112,16,16,18,18,72,504,
%U A140821 252,252,504,72,18,18
%N A140821 Coefficients of Hodge diamond GCD binomial product 'X' matrices as polynomials: matrix example; M={{2,0,2}. {0,2,0], {2,0,2}: M(d, x, y)= Sum[Sum[If[n == m, GCD[d - 1, m - 1], If[n == d - m + 1, GCD[d - 1, n - 1], 0]]*x^(n - 1)*y^(m - 1), {n, 1, d}], {m, 1, d}] .
%e A140821 {},
%e A140821 {2, 2},
%e A140821 {4, 2, 4},
%e A140821 {6, 6, 6, 6},
%e A140821 {8, 8, 12, 8, 8},
%e A140821 {10, 10, 20, 20, 10, 10},
%e A140821 {12, 12, 60, 60, 60, 12, 12},
%e A140821 {14, 14, 42, 70, 70, 42, 14, 14},
%e A140821 {16, 16, 112, 112, 280, 112, 112, 16, 16},
%e A140821 {18, 18, 72, 504, 252, 252, 504, 72, 18, 18}
%t A140821 M[d_, x_, y_] := Sum[Sum[If[n == m, Binomial[d - 1, m - 1]* GCD[d - 1, m - 1], If[n == d - m + 1, Binomial[d - 1, n - 1] *GCD[d - 1, n - 1], 0]]*x^(n - 1)*y^(m - 1), {n, d}], {m, d}];
%t A140821 Flatten@ Table[CoefficientList[M[d, x, 1], x], {d, 10}]
%Y A140821 Cf. A140685.
%K A140821 nonn,uned,tabf
%O A140821 1,1
%A A140821 _Roger L. Bagula_ and _Mats Granvik_, Jul 16 2008