A353511 Positions of odd terms in A001001, where A001001(n) = Sum_{d|n} d*sigma(d).

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

Offset

1,2

Comments

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.

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

The asymptotic density of this sequence is Pi^2/12 = 0.822467... (A072691). - Amiram Eldar, Oct 23 2023

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Mathematica

Position[Array[DivisorSum[#, # DivisorSigma[1, #] &] &, 94], _?OddQ][[All, 1]] (* Michael De Vlieger, May 03 2022 *)

Prog

(PARI)
A001001(n) = sumdivmult(n, d, sigma(d)*d);
A353628(n) = (A001001(n)%2);
isA353511(n) = A353628(n);

Crossrefs

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

Sequence in context: A168183 A043094 A023803 * A122132 A347248 A347243

Adjacent sequences: A353508 A353509 A353510 * A353512 A353513 A353514

Keyword

nonn

Author

Antti Karttunen, May 03 2022

Status

approved