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A353511
Positions of odd terms in A001001, where A001001(n) = Sum_{d|n} d*sigma(d).
3
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
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
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 03 2022
STATUS
approved