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A347874 Odd composites for which A342926(n) is even and A342926(2*n) is a multiple of 3. 4
45, 153, 261, 325, 369, 405, 441, 477, 801, 909, 925, 1017, 1233, 1341, 1377, 1521, 1525, 1557, 1573, 1773, 1825, 2097, 2205, 2313, 2349, 2401, 2421, 2425, 2529, 2637, 2725, 2853, 3177, 3249, 3321, 3501, 3609, 3645, 3757, 3825, 3925, 4041, 4149, 4293, 4477, 4525, 4581, 4689, 4825, 5013, 5121, 5337, 5445, 5553, 5725 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers k for which A347871(k) = 0 and A347883(2*k) = 0.

This is not a subsequence of A228058. The terms that do not occur there: 441, 1521, 2401, 3249, 8649, 16641, 28561, 35721, etc., seem all to be squares. Terms of A228058 missing from this sequence are: 117, 245, 333, 425, 549, 605, 637, 657, 725, etc. (See A351574.)

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..20000

Index entries for sequences where odd perfect numbers must occur, if they exist at all

MATHEMATICA

ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); f[n_] := ad[DivisorSigma[1, n]] - n; Select[Range[1, 5725, 2], CompositeQ[#] && EvenQ[f[#]] && Divisible[f[2*#], 3] &] (* Amiram Eldar, Sep 18 2021 *)

PROG

(PARI)

A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1]));

A342926(n) = (A003415(sigma(n))-n);

isA347874(n) = ((n%2)&&!isprime(n)&&!(A342926(n)%2)&&!(A342926(2*n)%3));

CROSSREFS

Cf. A000203, A003415, A228058, A342925, A342926, A347871, A347883, A351574.

Intersection of A347872 and A351562.

Sequence in context: A044377 A044758 A053743 * A234336 A173371 A288669

Adjacent sequences:  A347871 A347872 A347873 * A347875 A347876 A347877

KEYWORD

nonn

AUTHOR

Antti Karttunen, Sep 18 2021

STATUS

approved

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Last modified May 21 06:36 EDT 2022. Contains 353889 sequences. (Running on oeis4.)