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A332458 Odd numbers k, not powers of primes, such that sigma(k) == 2 modulo 8 and sigma(sigma(k)) == 6 modulo 8. 5

%I #10 Sep 08 2022 08:46:25

%S 4041,5193,15633,25181,25497,26645,30249,36441,36517,40817,47045,

%T 53577,54513,85697,87273,92889,93393,94761,95913,97281,111609,129681,

%U 136233,143433,151713,161257,162441,163377,165897,171197,177129,210033,212697,213849,222993,228977,229833,232897,238041,245673,246969,250137,260577

%N Odd numbers k, not powers of primes, such that sigma(k) == 2 modulo 8 and sigma(sigma(k)) == 6 modulo 8.

%H Antti Karttunen, <a href="/A332458/b332458.txt">Table of n, a(n) for n = 1..9315</a>

%H <a href="/index/O#opnseqs">Index entries for sequences where any odd perfect numbers must occur</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%o (PARI) isA332458(n) = if(!(n%2)||isprimepower(n),0, my(s=sigma(n)); ((2==(s%8)) && (6==(sigma(s)%8))));

%o (Magma) [k:k in [3..270000 by 2]| not IsPrimePower(k) and DivisorSigma(1,k) mod 8 eq 2 and DivisorSigma(1, DivisorSigma(1,k)) mod 8 eq 6]; // _Marius A. Burtea_, Feb 15 2020

%Y Cf. A000203, A000961, A051027.

%Y Intersection of A228058 and A332457; intersection of A332456 and A332228.

%Y Cf. also A332445.

%K nonn

%O 1,1

%A _Antti Karttunen_, Feb 15 2020

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)