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Numbers k such that floor(Sum_{d|k} 1 / sigma(d)) = 3.
9

%I #15 Sep 08 2022 08:46:15

%S 110880,166320,221760,277200,327600,332640,360360,388080,393120,

%T 415800,443520,471240,480480,491400,498960,526680,540540,554400,

%U 556920,582120,589680,600600,622440,637560,655200,665280,693000,720720,776160,786240,803880,831600

%N Numbers k such that floor(Sum_{d|k} 1 / sigma(d)) = 3.

%C Numbers k such that A265710(k) = floor(A265708(k) / A069934(k)) = floor(A265709(k) / A265710(k)) = 3.

%C See A265714(n) = the smallest number k such that floor(Sum_{d|k} 1/sigma(d)) = n.

%H Amiram Eldar, <a href="/A265713/b265713.txt">Table of n, a(n) for n = 1..10000</a>

%e 110880 is a term because floor(Sum_{d|110880} 1/sigma(d)) = floor(22333/7440) = 3.

%t Select[Range[10^5, 9*10^5], Floor[Sum[1/DivisorSigma[1, d], {d, Divisors@ #}]] == 3 &] (* _Michael De Vlieger_, Dec 31 2015 *)

%o (Magma) [n: n in [1..1000000] | Floor(&+[1/SumOfDivisors(d): d in Divisors(n)]) eq 3]

%o (PARI) isok(n) = floor(sumdiv(n, d, 1/sigma(d))) == 3; \\ _Michel Marcus_, Dec 27 2015

%Y Cf. A069934, A000203, A265708, A265709, A265710, A265711, A265712, A265714, A266227, A266228.

%K nonn

%O 1,1

%A _Jaroslav Krizek_, Dec 25 2015