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 A144733 #13 Jul 29 2019 20:15:08
%S A144733 1,-3,2,-3,-3,4,-1,-4,-1,4,-3,-3,-3,-3,8,1,-2,-4,-2,1,4,-3,-3,-3,-3,
%T A144733 -3,-3,12,-1,0,-1,-8,-1,0,-1,8,-1,-1,-6,-1,-1,-6,-1,-1,12,1,-2,1,-2,
%U A144733 -8,-2,1,-2,1,8,-3,-3,-3,-3,-3,-3,-3,-3,-3,-3,20
%N A144733 Triangle read by rows, 2*A054533 - A054521.
%C A144733 Right border = A140434: (1, 2, 4, 4, 8, 4, 12,...).
%C A144733 Left border = A133695: (1, -3, -3, -1, -3, 1, -3, -1,...)
%C A144733 Row sums = A000010, with negative signs after the first 1: (1, -1, -2, -2, -4, -2, -6,...).
%F A144733 Triangle read by rows, 2*A054533 - A054521; as infinite lower triangular matrices.
%F A144733 T(n,k) = -I(gcd(n,k) = 1) + 2 * Sum_{d|gcd(n,k)} d * mu(n/d) for n >= 1 and 1 <= k <= n, where I(condition) = 1 if the condition holds, and 0 otherwise. - _Petros Hadjicostas_, Jul 29 2019
%e A144733 First few rows of the triangle =
%e A144733 1;
%e A144733 -3, 2;
%e A144733 -3, -3, 4;
%e A144733 -1, -4, -1, 4;
%e A144733 -3, -3, -3, -3, 8;
%e A144733 1, -2, -4, -2, 1, 4;
%e A144733 -3, -3, -3, -3, -3, -3, 12;
%e A144733 -1, 0, -1, -8 -1, 0, -1, 8;
%e A144733 -1, -1, -6, -1, -1, -6, -1, -1, 12;
%e A144733 1, -2, 1, -2, -8, -2, 1, -2, 1, 8;
%e A144733 -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, 20;
%e A144733 ...
%Y A144733 Cf. A000010, A054521, A054532, A054533, A054534, A054535, A140434, A133695.
%K A144733 tabl,sign
%O A144733 1,2
%A A144733 _Gary W. Adamson_, Sep 20 2008