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 A140435 #16 Sep 14 2021 08:56:02
%S A140435 0,1,1,3,1,7,1,7,5,11,1,15,1,15,13,15,1,23,1,23,17,23,1,31,9,27,17,31,
%T A140435 1,43,1,31,25,35,21,47,1,39,29,47,1,59,1,47,41,47,1,63,13,59,37,55,1,
%U A140435 71,29,63,41,59,1,87,1,63,53,63,33,91,1,71,49,91,1,95,1,75,69,79,33,107,1,95,53
%N A140435 Number of new lattice points created at each step in an n X n grid that are not visible.
%F A140435 G.f.: -Sum_{k>=2} mu(k) * x^k * (1 + x^k) / (1 - x^k)^2. - _Ilya Gutkovskiy_, Sep 14 2021
%t A140435 g[n_] := Table[ #^2 &[m], {m, 1, n + 1}] - FoldList[Plus, 1, 2 Array[EulerPhi, n, 2]] - Most[Flatten[ Append[{0}, Table[ #^2 &[m], {m, 1, n + 1}] - FoldList[Plus, 1, 2 Array[EulerPhi, n, 2]]]]]; g[80]
%Y A140435 Cf. A018805, A100613 and A140434.
%K A140435 nonn
%O A140435 1,4
%A A140435 _Gregg Whisler_, Jun 25 2008
%E A140435 More terms from _Robert G. Wilson v_, Jan 17 2011