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A347880 Numbers k such that A342926(k) is a multiple of 3. 3
4, 5, 8, 14, 16, 20, 23, 25, 26, 30, 38, 41, 49, 51, 59, 62, 64, 66, 74, 77, 80, 86, 90, 92, 96, 102, 108, 113, 120, 122, 124, 127, 131, 134, 138, 143, 146, 149, 153, 158, 159, 164, 165, 167, 169, 174, 194, 196, 198, 200, 203, 204, 206, 209, 210, 213, 217, 218, 223, 236, 239, 243, 246, 254, 255, 257, 264, 267, 270 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[270], Divisible[ad[DivisorSigma[1, #]] - #, 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);
isA347880(n) = !(A342926(n)%3);
CROSSREFS
Positions of zeros in A347883.
Cf. A005820, A342923 (subsequences).
Cf. also A347872.
Sequence in context: A242014 A145488 A050892 * A274167 A145265 A244161
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 18 2021
STATUS
approved

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Last modified March 29 06:34 EDT 2024. Contains 371265 sequences. (Running on oeis4.)