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 A378219 #6 Nov 23 2024 10:45:13
%S A378219 1,-3,-3,2,-3,7,-3,0,2,7,-3,-4,-3,7,7,0,-3,-4,-3,-4,7,7,-3,0,2,7,0,-4,
%T A378219 -3,-15,-3,0,7,7,7,2,-3,7,7,0,-3,-15,-3,-4,-4,7,-3,0,2,-4,7,-4,-3,0,7,
%U A378219 0,7,7,-3,8,-3,7,-4,0,7,-15,-3,-4,7,-15,-3,0,-3,7,-4,-4,7,-15,-3,0,0,7,-3,8,7,7,7,0,-3,8,7
%N A378219 Dirichlet inverse of A253249.
%H A378219 Antti Karttunen, <a href="/A378219/b378219.txt">Table of n, a(n) for n = 1..20000</a>
%F A378219 a(1) = 1, and for n > 1, a(n) = -Sum_{d|n, d<n} A253249(n/d) * a(d).
%o A378219 (PARI)
%o A378219 A074206(n) = if(n>1, sumdiv(n, i, if(i<n, A074206(i))), n); \\ From A074206
%o A378219 A253249(n) = if(1==n,n,4*A074206(n)-1);
%o A378219 memoA378219 = Map();
%o A378219 A378219(n) = if(1==n,1,my(v); if(mapisdefined(memoA378219,n,&v), v, v = -sumdiv(n,d,if(d<n,A253249(n/d)*A378219(d),0)); mapput(memoA378219,n,v); (v)));
%Y A378219 Cf. A074206, A253249.
%K A378219 sign
%O A378219 1,2
%A A378219 _Antti Karttunen_, Nov 23 2024