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 A344931 #35 Jun 23 2024 01:45:58
%S A344931 0,0,3,0,0,3,7,0,3,0,0,3,13,7,3,0,0,3,19,0,10,0,0,3,0,13,3,7,29,3,0,0,
%T A344931 3,0,7,3,37,19,16,0,0,10,43,0,3,0,0,3,7,0,3,13,53,3,0,7,22,29,0,3,61,
%U A344931 0,10,0,13,3,0,0,3,7,71,3,0,37,3,19,7,16,79,0,3,0,0,10,0,43,32
%N A344931 Sum of the distinct even-indexed prime divisors, p_{2k}, of n.
%C A344931 Inverse Möbius transform of n * c(n) * ((pi(n)+1) mod 2), where c(n) is the prime characteristic (A010051). - _Wesley Ivan Hurt_, Jun 23 2024
%H A344931 Martin Ehrenstein, <a href="/A344931/b344931.txt">Table of n, a(n) for n = 1..20000</a>
%F A344931 a(n) = Sum_{p|n} p * ((pi(p)+1) mod 2).
%F A344931 G.f.: Sum_{k>=1} prime(2*k) * x^prime(2*k) / (1 - x^prime(2*k)). - _Ilya Gutkovskiy_, Oct 24 2023
%F A344931 a(n) = Sum_{d|n} d * c(d) * ((pi(d)+1) mod 2), where c = A010051. - _Wesley Ivan Hurt_, Jun 23 2024
%e A344931 a(12) = Sum_{p|12} p * ((pi(p)+1) mod 2) = 2*0 + 3*1 = 3.
%t A344931 Table[Sum[k*Mod[PrimePi[k] + 1, 2] (PrimePi[k] - PrimePi[k - 1]) (1 - Ceiling[n/k] + Floor[n/k]), {k, n}], {n, 100}]
%o A344931 (PARI) a(n) = my(f=factor(n)); sum(k=1, #f~, if (!(primepi(f[k,1]) % 2), f[k,1])); \\ _Michel Marcus_, Jun 12 2021
%Y A344931 Cf. A000720 (pi), A008472 (sopf), A005074, A324966.
%Y A344931 Cf. A344908 (sum of distinct odd-indexed prime divisors).
%K A344931 nonn
%O A344931 1,3
%A A344931 _Wesley Ivan Hurt_, Jun 02 2021