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 A377984 #7 Nov 16 2024 18:48:30
%S A377984 1,3,3,5,5,9,5,3,1,15,11,11,11,15,13,-19,17,3,17,21,9,33,19,-15,13,33,
%T A377984 -45,13,29,39,27,-117,31,51,19,-43,35,51,27,-9,41,27,41,51,-19,57,43,
%U A377984 -157,-7,39,49,43,49,-135,53,-57,45,87,59,21,57,81,-67,-475,49,93,65,81,47,57,71,-285,69,105,3,73,49,81
%N A377984 a(n) = 2*sigma(n) - A003961(n), where sigma is the sum of divisors function and A003961 is fully multiplicative function with a(prime(i)) = prime(i+1).
%H A377984 Antti Karttunen, <a href="/A377984/b377984.txt">Table of n, a(n) for n = 1..20000</a>
%H A377984 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>
%H A377984 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%o A377984 (PARI)
%o A377984 A003961(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };
%o A377984 A377984(n) = (2*sigma(n) - A003961(n));
%Y A377984 Cf. A000203, A003961.
%Y A377984 Cf. A337378 (positions of negative terms), A337379 (of positive terms), A337380 (their characteristic function), A377985 (Möbius transform).
%K A377984 sign
%O A377984 1,2
%A A377984 _Antti Karttunen_, Nov 16 2024