cp's OEIS Frontend

A076231 Numbers k such that sigma(k)/k, sigma_3(k)/k and sigma_5(k)/k are all integers.

%I A076231 #20 May 09 2024 02:55:25
%S A076231 1,6,120,672,8128,30240,32760,33550336,459818240,1379454720,
%T A076231 1476304896,8589869056,31998395520,51001180160,66433720320,
%U A076231 137438691328,153003540480,403031236608,30823866178560,796928461056000,6088728021160320,14942123276641920,212517062615531520
%N A076231 Numbers k such that sigma(k)/k, sigma_3(k)/k and sigma_5(k)/k are all integers.
%H A076231 Amiram Eldar, <a href="/A076231/b076231.txt">Table of n, a(n) for n = 1..86</a>
%o A076231 (PARI) isok(n) = !(sigma(n) % n) && !(sigma(n, 3) % n) && !(sigma(n, 5) % n); \\ _Michel Marcus_, Dec 26 2013
%Y A076231 Intersection of A007691, A046763 and A055709.
%Y A076231 Cf. A000203, A001158, A001160, A007691, A046763, A055709, A076233, A076234.
%K A076231 nonn
%O A076231 1,2
%A A076231 _Labos Elemer_, Oct 03 2002
%E A076231 a(16)-a(20) from _Donovan Johnson_, May 08 2010
%E A076231 a(21)-a(23) from _Amiram Eldar_, May 09 2024