cp's OEIS Frontend

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

%I A332458 #10 Sep 08 2022 08:46:25
%S A332458 4041,5193,15633,25181,25497,26645,30249,36441,36517,40817,47045,
%T A332458 53577,54513,85697,87273,92889,93393,94761,95913,97281,111609,129681,
%U A332458 136233,143433,151713,161257,162441,163377,165897,171197,177129,210033,212697,213849,222993,228977,229833,232897,238041,245673,246969,250137,260577
%N A332458 Odd numbers k, not powers of primes, such that sigma(k) == 2 modulo 8 and sigma(sigma(k)) == 6 modulo 8.
%H A332458 Antti Karttunen, <a href="/A332458/b332458.txt">Table of n, a(n) for n = 1..9315</a>
%H A332458 <a href="/index/O#opnseqs">Index entries for sequences where any odd perfect numbers must occur</a>
%H A332458 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%o A332458 (PARI) isA332458(n) = if(!(n%2)||isprimepower(n),0, my(s=sigma(n)); ((2==(s%8)) && (6==(sigma(s)%8))));
%o A332458 (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 A332458 Cf. A000203, A000961, A051027.
%Y A332458 Intersection of A228058 and A332457; intersection of A332456 and A332228.
%Y A332458 Cf. also A332445.
%K A332458 nonn
%O A332458 1,1
%A A332458 _Antti Karttunen_, Feb 15 2020