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 A140819 #17 Jan 03 2024 09:55:41
%S A140819 0,2,2,4,1,4,6,2,2,6,8,2,2,2,8,10,2,2,2,2,10,12,2,4,3,4,2,12,14,2,2,2,
%T A140819 2,2,2,14,16,2,4,2,4,2,4,2,16,18,2,2,6,2,2,6,2,2,18
%N A140819 Triangle read by rows: T(n, m) = m if 2*m = n, otherwise 2*gcd(n, m).
%e A140819 {0},
%e A140819 {2, 2},
%e A140819 {4, 1, 4},
%e A140819 {6, 2, 2, 6},
%e A140819 {8, 2, 2, 2, 8},
%e A140819 {10, 2, 2, 2, 2, 10},
%e A140819 {12, 2, 4, 3, 4, 2, 12},
%e A140819 {14, 2, 2, 2, 2, 2, 2, 14},
%e A140819 {16, 2, 4, 2, 4, 2, 4, 2, 16},
%e A140819 {18, 2, 2, 6, 2, 2, 6, 2, 2, 18}
%t A140819 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}]
%t A140819 Table[CoefficientList[M[d, x, 1], x], {d, 1, 10}]
%t A140819 Flatten[%]
%t A140819 Table[Apply[Plus, CoefficientList[M[d, x, 1], x]], {d, 1, 10}]
%Y A140819 Cf. A109004, A140685.
%K A140819 nonn,tabl
%O A140819 0,2
%A A140819 _Roger L. Bagula_ and _Mats Granvik_, Jul 16 2008
%E A140819 Definition simplified by the editors of the OEIS, Jan 03 2024