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 A380584 #12 Feb 16 2025 08:34:07
%S A380584 1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,5,1,2,1,3,1,2,2,4,1,2,1,3,1,3,2,6,1,2,
%T A380584 2,3,1,2,1,4,1,3,1,3,1,4,3,5,1,2,1,3,1,2,2,4,1,2,1,5,1,4,1,7,1,4,1,3,
%U A380584 1,5,3,4,1,2,1,3,2,2,2,5,1,2,2,5,1,2,1,4,1,2,1,6,1,6,2,6,1,2,1,3
%N A380584 Number of positive integers <= n that have the same sum of odd divisors as n.
%C A380584 Ordinal transform of A000593.
%H A380584 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/OddDivisorFunction.html">Odd Divisor Function</a>.
%F A380584 a(n) = |{j <= n : A000593(j) = A000593(n)}|.
%t A380584 Table[Length[Select[Range[n], Sum[Mod[d, 2] d, {d, Divisors[#]}] == Sum[Mod[d, 2] d, {d, Divisors[n]}] &]], {n, 1, 100}]
%Y A380584 Cf. A000593, A263025, A337557, A380653, A380654.
%K A380584 nonn
%O A380584 1,2
%A A380584 _Ilya Gutkovskiy_, Jan 30 2025