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 A373923 #10 Sep 13 2024 15:57:32
%S A373923 1,0,2,1,0,0,2,2,3,0,0,0,2,2,2,3,0,0,2,2,4,0,0,0,-1,0,2,2,2,2,0,2,0,
%T A373923 -2,0,-1,2,2,4,4,0,2,2,2,4,0,0,0,1,-2,0,0,2,0,0,4,4,2,0,2,2,0,6,3,2,0,
%U A373923 0,-2,0,0,2,0,0,0,0,2,0,0,2,6,3,0,0,0,-2,0,2,2
%N A373923 a(n) = Sum_{d|n} (-1)^pi(d).
%C A373923 Inverse Möbius transform of (-1)^pi(n) (A065357).
%H A373923 Robert Israel, <a href="/A373923/b373923.txt">Table of n, a(n) for n = 1..10000</a>
%p A373923 f:= proc(n) local d; add((-1)^numtheory:-pi(d),d=numtheory:-divisors(n)) end proc:
%p A373923 map(f, [$1..100]); # _Robert Israel_, Sep 13 2024
%t A373923 Table[DivisorSum[n, (-1)^PrimePi[#] &], {n, 100}]
%Y A373923 Cf. A000720 (pi), A065357, A065358 (Jacob's Ladder sequence).
%K A373923 sign
%O A373923 1,3
%A A373923 _Wesley Ivan Hurt_, Jun 22 2024