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A347878
Numbers k for which A003415(sigma(k)) is even.
4
1, 3, 6, 7, 8, 11, 12, 14, 15, 18, 19, 21, 22, 23, 24, 27, 28, 30, 31, 33, 35, 36, 38, 39, 42, 43, 44, 46, 47, 48, 49, 50, 51, 54, 55, 56, 57, 59, 60, 62, 63, 65, 66, 67, 69, 70, 71, 75, 76, 77, 78, 79, 81, 83, 84, 85, 86, 87, 88, 91, 92, 93, 94, 95, 96, 99, 100, 102, 103, 105, 107, 108, 110, 111, 112, 114, 115
OFFSET
1,2
COMMENTS
Numbers k such that A342925(k) == 0 (mod 2).
Odd squares present are terms of A347886 squared.
Conjecture: A342923 is a subsequence of this sequence. See comments in A347870.
MATHEMATICA
ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[115], EvenQ[ad[DivisorSigma[1, #]]] &] (* Amiram Eldar, Sep 19 2021 *)
PROG
(PARI) isA347878(n) = !A347870(n);
CROSSREFS
Positions of zeros in A347870.
Sequence in context: A374483 A298980 A206586 * A289176 A277851 A047557
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 19 2021
STATUS
approved