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 A068378 Numbers n such that sigma(n)^2 > 9*sigma_2(n) where sigma_2(n) is the sum of squares over the divisors of n. 1

%I #12 Aug 14 2019 08:25:47

%S 5040,7560,10080,12600,13860,15120,17640,18480,20160,21840,22680,

%T 25200,27720,30240,32760,35280,36960,37800,39600,40320,41580,42840,

%U 43680,45360,46200,47520,47880,49140,50400,51480,52920,54600,55440,56160

%N Numbers n such that sigma(n)^2 > 9*sigma_2(n) where sigma_2(n) is the sum of squares over the divisors of n.

%H Amiram Eldar, <a href="/A068378/b068378.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[60000],DivisorSigma[1,#]^2>9DivisorSigma[2,#]&] (* _Harvey P. Dale_, Mar 20 2015 *)

%o (PARI) for(n=1,1000,if(sigma(n)^2>9*sumdiv(n,k,k^2),print1(n,",")))

%Y Cf. A000203, A001157.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Apr 04 2002

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Last modified September 26 08:16 EDT 2023. Contains 365654 sequences. (Running on oeis4.)