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A347873 Numbers k such that k and A003415(sigma(k)) are of different parity. 4
1, 2, 3, 4, 7, 10, 11, 15, 16, 19, 20, 21, 23, 26, 27, 31, 32, 33, 34, 35, 39, 40, 43, 47, 49, 51, 52, 55, 57, 58, 59, 63, 64, 65, 67, 68, 69, 71, 72, 74, 75, 77, 79, 80, 81, 82, 83, 85, 87, 90, 91, 93, 95, 98, 99, 103, 104, 105, 106, 107, 111, 115, 116, 119, 121, 122, 123, 125, 127, 128, 129, 131, 133, 135, 136 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers k for which A347870(k) differs from A000035(k).

LINKS

Table of n, a(n) for n=1..75.

MATHEMATICA

ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[136], Mod[ad[DivisorSigma[1, #]], 2] != Mod[#, 2] &] (* Amiram Eldar, Sep 18 2021 *)

CROSSREFS

Cf. A000035, A000203, A003415, A342925, A347870.

Positions of ones in A347871 (the characteristic function). A347872 gives the complement.

Sequence in context: A266510 A266540 A342790 * A139759 A030292 A204231

Adjacent sequences:  A347870 A347871 A347872 * A347874 A347875 A347876

KEYWORD

nonn

AUTHOR

Antti Karttunen, Sep 17 2021

STATUS

approved

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Last modified October 18 23:44 EDT 2021. Contains 348071 sequences. (Running on oeis4.)