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A347872 Numbers k such that k and A003415(sigma(k)) have the same parity. 9

%I #11 Sep 18 2021 22:04:12

%S 5,6,8,9,12,13,14,17,18,22,24,25,28,29,30,36,37,38,41,42,44,45,46,48,

%T 50,53,54,56,60,61,62,66,70,73,76,78,84,86,88,89,92,94,96,97,100,101,

%U 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

%N Numbers k such that k and A003415(sigma(k)) have the same parity.

%C Numbers k for which A347870(k) is equal to A000035(k).

%H <a href="/index/O#opnseqs">Index entries for sequences where odd perfect numbers must occur, if they exist at all</a>

%t 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 *)

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

%Y Positions of zeros in A347871. Cf. A347873 for complement.

%Y Cf. A000396, A342922, A347874 (subsequences).

%Y Cf. also A347883.

%K nonn

%O 1,1

%A _Antti Karttunen_, Sep 17 2021

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Last modified March 29 06:15 EDT 2024. Contains 371265 sequences. (Running on oeis4.)