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A347872
Numbers k such that k and A003415(sigma(k)) have the same parity.
10
5, 6, 8, 9, 12, 13, 14, 17, 18, 22, 24, 25, 28, 29, 30, 36, 37, 38, 41, 42, 44, 45, 46, 48, 50, 53, 54, 56, 60, 61, 62, 66, 70, 73, 76, 78, 84, 86, 88, 89, 92, 94, 96, 97, 100, 101, 102, 108, 109, 110, 112, 113, 114, 117, 118, 120, 124, 126, 130, 132, 134, 137, 138, 140, 142, 144, 149, 150, 152, 153, 154, 156, 157
OFFSET
1,1
COMMENTS
Numbers k for which A347870(k) is equal to A000035(k).
MAPLE
ader:= proc(n) local F, t;
F:= ifactors(n)[2];
add(t[2]*n/t[1], t= F)
end proc:
filter:= n -> n - ader(numtheory:-sigma(n)) mod 2 = 0:
select(filter, [$1..1000]); # Robert Israel, Sep 11 2024
MATHEMATICA
ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[157], Mod[ad[DivisorSigma[1, #]], 2] == Mod[#, 2] &] (* Amiram Eldar, Sep 18 2021 *)
CROSSREFS
Positions of zeros in A347871. Cf. A347873 for complement.
Cf. A000396, A342922, A347874 (subsequences).
Cf. also A347883.
Sequence in context: A158698 A120174 A184817 * A191355 A337143 A047439
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 17 2021
STATUS
approved