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 A378213 #7 Nov 22 2024 11:01:11
%S A378213 1,-2,-2,0,-2,3,-2,2,0,3,-2,2,-2,3,3,-1,-2,2,-2,2,3,3,-2,-4,0,3,2,2,
%T A378213 -2,-2,-2,0,3,3,3,-3,-2,3,3,-4,-2,-2,-2,2,2,3,-2,0,0,2,3,2,-2,-4,3,-4,
%U A378213 3,3,-2,-6,-2,3,2,0,3,-2,-2,2,3,-2,-2,-2,-2,3,2,2,3,-2,-2,0,-1,3,-2,-6,3,3,3,-4,-2,-6,3,2,3,3,3,1
%N A378213 Dirichlet inverse of A140773.
%H A378213 Antti Karttunen, <a href="/A378213/b378213.txt">Table of n, a(n) for n = 1..20000</a>
%F A378213 a(1) = 1, and for n > 1, a(n) = -Sum_{d|n, d<n} A140773(n/d) * a(d).
%o A378213 (PARI)
%o A378213 A065043(n) = (1 - (bigomega(n)%2));
%o A378213 A038548(n) = sumdiv(n,d,A065043(d));
%o A378213 A140773(n) = sumdiv(n,d,A038548(d));
%o A378213 memoA378213 = Map();
%o A378213 A378213(n) = if(1==n,1,my(v); if(mapisdefined(memoA378213,n,&v), v, v = -sumdiv(n,d,if(d<n,A140773(n/d)*A378213(d),0)); mapput(memoA378213,n,v); (v)));
%Y A378213 Cf. A140773, A378214, A378215 (parity of terms).
%K A378213 sign
%O A378213 1,2
%A A378213 _Antti Karttunen_, Nov 22 2024