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 A378214 #11 Jul 07 2025 10:20:36
%S A378214 1,0,0,0,0,-1,0,0,0,-1,0,0,0,-1,-1,-1,0,0,0,0,-1,-1,0,0,0,-1,0,0,0,0,
%T A378214 0,0,-1,-1,-1,1,0,-1,-1,0,0,0,0,0,0,-1,0,0,0,0,-1,0,0,0,-1,0,-1,-1,0,
%U A378214 2,0,-1,0,0,-1,0,0,0,-1,0,0,0,0,-1,0,0,-1,0,0,0,-1,-1,0,2,-1,-1,-1,0,0,2,-1,0,-1,-1,-1,1,0,0,0,1
%N A378214 Dirichlet inverse of A369255, where A369255(n) = A140773(n) mod 2.
%H A378214 Antti Karttunen, <a href="/A378214/b378214.txt">Table of n, a(n) for n = 1..20000</a>
%F A378214 a(1) = 1, and for n > 1, a(n) = -Sum_{d|n, d<n} A369255(n/d) * a(d).
%o A378214 (PARI)
%o A378214 A065043(n) = (1 - (bigomega(n)%2));
%o A378214 A038548(n) = sumdiv(n,d,A065043(d));
%o A378214 A140773(n) = sumdiv(n,d,A038548(d));
%o A378214 A369255(n) = (A140773(n)%2);
%o A378214 memoA378214 = Map();
%o A378214 A378214(n) = if(1==n,1,my(v); if(mapisdefined(memoA378214,n,&v), v, v = -sumdiv(n,d,if(d<n,A369255(n/d)*A378214(d),0)); mapput(memoA378214,n,v); (v)));
%Y A378214 Cf. A140773, A369255, A378213, A378215 (parity of terms).
%Y A378214 Cf. also conjectured formula in A252505.
%K A378214 sign
%O A378214 1,60
%A A378214 _Antti Karttunen_, Nov 22 2024