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 A385628 #8 Jul 05 2025 09:36:40
%S A385628 1,1,4,5,1,4,8,13,13,11,1,8,14,22,19,29,1,13,20,35,32,23,1,16,1,14,13,
%T A385628 26,30,59,1,29,4,1,8,17,38,58,56,83,1,46,44,71,73,47,1,32,8,11,4,18,
%U A385628 54,67,56,90,80,88,1,83,62,63,104,93,79,92,1,5,4,32,72,97,1,38,19,62,8,56,80,179,94,83,1,50,1,44,33,79,90,203,112,143,97,95,115
%N A385628 Sum of the divisors d of n with an even number of primes not exceeding d.
%C A385628 Inverse Möbius transform of n * ((pi(n)+1) mod 2) = n * A131377(n).
%F A385628 a(n) = Sum_{d|n} d * ((pi(d)+1) mod 2).
%F A385628 a(n) = A000203(n) - A385625(n).
%e A385628 The sum of the divisors d of 16 such that pi(d) is even gives 1 + 4 + 8 + 16 = 29.
%t A385628 Table[Sum[d*Mod[PrimePi[d] + 1, 2], {d, Divisors[n]}], {n, 100}]
%Y A385628 Cf. A000203 (sigma), A000720 (pi), A131377, A345220, A385625.
%K A385628 nonn,easy
%O A385628 1,3
%A A385628 _Wesley Ivan Hurt_, Jul 05 2025