login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

Numbers n such that phi(n + 1) | sigma(n) for n congruent to 1 (mod 3).
1

%I #30 Feb 23 2018 18:54:03

%S 1,7,28,31,55,94,127,265,322,385,406,649,1504,1624,1990,2488,3115,

%T 3154,4402,5269,6265,6460,7258,7384,7579,8191,8455,8995,9229,9799,

%U 11815,12466,13114,13243,14146,15385,16309,16849,17731,20995,23359

%N Numbers n such that phi(n + 1) | sigma(n) for n congruent to 1 (mod 3).

%H Andrew Howroyd, <a href="/A015817/b015817.txt">Table of n, a(n) for n = 1..100</a>

%t Select[Range[1, 100000, 3], Divisible[DivisorSigma[1, #], EulerPhi[1 + #]] &] (* _David Nacin_, Mar 01 2012 *)

%o (PARI) is(n)=n%3==1 && sigma(n)%(eulerphi(n)+1)==0 \\ _Charles R Greathouse IV_, Sep 25 2012

%K nonn

%O 1,2

%A _Robert G. Wilson v_