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 A023197 Numbers k such that sigma(k) >= 3*k. 15

%I

%S 120,180,240,360,420,480,504,540,600,660,672,720,780,840,900,960,1008,

%T 1080,1200,1260,1320,1344,1440,1512,1560,1584,1620,1680,1800,1848,

%U 1872,1890,1920,1980,2016,2040,2100,2160,2184,2280,2340,2352,2376,2400,2520

%N Numbers k such that sigma(k) >= 3*k.

%C Sometimes called 3-abundant numbers (but compare the comments in A033880). The first odd number is A119240(3) = 1018976683725. - _T. D. Noe_, Mar 31 2011

%D Melvyn B. Nathanson, Elementary Methods in Number Theory, Springer, 2000, p 260.

%H T. D. Noe, <a href="/A023197/b023197.txt">Table of n, a(n) for n = 1..10000</a>

%H Richard Laatsch, <a href="http://www.jstor.org/stable/2690424">Measuring the Abundancy of Integers</a>, Mathematics Magazine, Vol. 59, No. 2 (1986), pp. 84-92, <a href="https://isidore.co/misc/Physics%20papers%20and%20books/Zotero/storage/99C5C5IC/Laatsch%20-%201986%20-%20Measuring%20the%20Abundancy%20of%20Integers.pdf">alternative link</a>.

%F A001221(a(n)) >= 3 (Laatsch, 1986). - _Amiram Eldar_, Nov 07 2020

%p select(t -> numtheory:-sigma(t) >= 3*t, [\$1..10000]); # _Robert Israel_, Dec 28 2014

%t Select[Range[10000], DivisorSigma[1,#] >= 3*#&] (* _Vladimir Joseph Stephan Orlovsky_, Apr 21 2010 *)

%Y Cf. A000203, A001221, A119240.

%Y See A033880 for definition of k-abundancy.

%K nonn

%O 1,1

%A _David W. Wilson_

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Last modified April 13 21:13 EDT 2021. Contains 342941 sequences. (Running on oeis4.)