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 A326938 #14 Nov 30 2020 03:58:09
%S A326938 1,-2,-4,0,-6,8,-8,0,3,12,-12,0,-14,16,24,0,-18,-6,-20,0,32,24,-24,0,
%T A326938 5,28,0,0,-30,-48,-32,0,48,36,48,0,-38,40,56,0,-42,-64,-44,0,-18,48,
%U A326938 -48,0,7,-10,72,0,-54,0,72,0,80,60,-60,0,-62,64,-24,0,84,-96,-68,0,96,-96
%N A326938 Dirichlet g.f.: 1 / (zeta(s) * zeta(s-1) * (1 - 2^(-s))).
%C A326938 Dirichlet inverse of A002131.
%H A326938 Amiram Eldar, <a href="/A326938/b326938.txt">Table of n, a(n) for n = 1..10000</a>
%F A326938 a(1) = 1; a(n) = -Sum_{d|n, d<n} A002131(n/d) * a(d).
%F A326938 a(n) = Sum_{d|n, n/d odd} mu(n/d) * mu(d) * d.
%F A326938 Multiplicative with a(2^e) = -2 if e = 1 and 0 otherwise, and a(p^e) = -(p+1) for e = 1, p for e = 2 and 0 if e > 2, for odd primes p. - _Amiram Eldar_, Nov 30 2020
%t A326938 a[1] = 1; a[n_] := -Sum[Total[Select[Divisors[n/d], OddQ[(n/d)/#] &]] a[d], {d, Most @ Divisors[n]}]; Table[a[n], {n, 1, 70}]
%t A326938 Table[DivisorSum[n, MoebiusMu[n/#] MoebiusMu[#] # &, OddQ[n/#] &], {n, 1, 70}]
%t A326938 f[2, e_] := -2*Boole[e == 1]; f[p_, e_] := Which[e == 1, -(p + 1), e == 2, p, e > 2, 0]; a[1] = 1; a[n_] := Times @@ (f @@@ FactorInteger[n]); Array[a, 100] (* _Amiram Eldar_, Nov 30 2020 *)
%o A326938 (PARI) a(n)={sumdiv(n, d, if(n/d%2, moebius(n/d)*moebius(d)*d))} \\ _Andrew Howroyd_, Oct 25 2019
%Y A326938 Cf. A002131, A008683, A046692, A327278.
%K A326938 sign,mult
%O A326938 1,2
%A A326938 _Ilya Gutkovskiy_, Oct 22 2019