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 A385625 #11 Jul 05 2025 09:36:13
%S A385625 0,2,0,2,5,8,0,2,0,7,11,20,0,2,5,2,17,26,0,7,0,13,23,44,30,28,27,30,0,
%T A385625 13,31,34,44,53,40,74,0,2,0,7,41,50,0,13,5,25,47,92,49,82,68,80,0,53,
%U A385625 16,30,0,2,59,85,0,33,0,34,5,52,67,121,92,112,0,98,73,76,105,78,88,112,0,7,27,43,83,174,107,88,87,101,0,31,0,25,31,49,5,124,97,149
%N A385625 Sum of the divisors d of n with an odd number of primes not exceeding d.
%C A385625 Inverse Möbius transform of n * (pi(n) mod 2) = n * A071986(n).
%F A385625 a(n) = Sum_{d|n} d * (pi(d) mod 2).
%F A385625 a(n) = A000203(n) - A385628(n).
%e A385625 The sum of the divisors d of 12 such that pi(d) is odd gives 2 + 6 + 12 = 20.
%t A385625 Table[Sum[d*Mod[PrimePi[d], 2], {d, Divisors[n]}], {n, 100}]
%Y A385625 Cf. A000203 (sigma), A000720 (pi), A071986, A345219, A385628.
%K A385625 nonn,easy
%O A385625 1,2
%A A385625 _Wesley Ivan Hurt_, Jul 05 2025