%I #14 Oct 23 2023 02:02:00

%S 1,2,3,4,5,6,7,8,10,11,12,13,14,15,16,17,19,20,21,22,23,24,26,28,29,

%T 30,31,32,33,34,35,37,38,39,40,41,42,43,44,46,47,48,51,52,53,55,56,57,

%U 58,59,60,61,62,64,65,66,67,68,69,70,71,73,74,76,77,78,79,80,81,82,83,84,85,86,87,88,89,91,92,93,94

%N Positions of odd terms in A001001, where A001001(n) = Sum_{d|n} d*sigma(d).

%C Differs from A122132 (which is a subsequence of this sequence) for the first time by having term 81. Sequence A353456 gives terms that are present here but not in the former. See also the discussion in A209635.

%C If k is present in the sequence, then 2*k and A000265(k) are present also.

%C The asymptotic density of this sequence is Pi^2/12 = 0.822467... (A072691). - _Amiram Eldar_, Oct 23 2023

%H Michael De Vlieger, <a href="/A353511/b353511.txt">Table of n, a(n) for n = 1..10000</a>

%t Position[Array[DivisorSum[#, # DivisorSigma[1, #] &] &, 94], _?OddQ][[All, 1]] (* _Michael De Vlieger_, May 03 2022 *)

%o (PARI)

%o A001001(n) = sumdivmult(n, d, sigma(d)*d);

%o A353628(n) = (A001001(n)%2);

%o isA353511(n) = A353628(n);

%Y Cf. A000265, A001001, A072691, A122132 (subsequence), A209635, A353456, A353628 (characteristic function).

%K nonn

%O 1,2

%A _Antti Karttunen_, May 03 2022