A058073 - OEIS

A058073

Numbers k such that sigma(k+1) divides sigma(k), where sigma(k) is the sum of positive divisors of k.

%I #24 Feb 19 2024 10:29:33

%S 12,14,70,88,180,204,206,220,957,1334,1364,1634,1750,1888,2685,2958,

%T 2974,4364,8142,8632,9114,12000,14664,14841,18414,18762,18873,19358,

%U 20118,20145,20712,24957,25194,30996,33998,36566,42818,45520,47940

%N Numbers k such that sigma(k+1) divides sigma(k), where sigma(k) is the sum of positive divisors of k.

%C The quotient (sigma(k)/sigma(k+1)) is equal to 1, 2, 3 or 4 for the first 5000 terms. - _Donovan Johnson_, Oct 21 2012

%H Donovan Johnson, <a href="/A058073/b058073.txt">Table of n, a(n) for n = 1..5000</a>

%e 12 is included because sigma(13) = 14 divides sigma(12) = 28.

%t Select[Range[50000], Mod[DivisorSigma[1, # ], DivisorSigma[1, # + 1]] == 0 &]

%K nonn

%O 1,1

%A _Leroy Quet_, Nov 11 2000

%E More terms from _Benoit Cloitre_, Jul 27 2002