A068422 - OEIS

%I #15 May 03 2019 19:24:13

%S 2,3,5,6,7,10,11,13,14,17,19,22,23,26,29,31,34,37,38,41,43,46,47,53,

%T 58,59,61,62,67,71,73,74,79,82,83,86,89,94,97,99,101,103,106,107,109,

%U 113,118,122,127,131,134,137,139,142,146,149,151,157,158,163,166,167,168

%N Numbers n such that n-phi(n) divides sigma(n).

%C If p is an odd prime, p and 2*p are in the sequence but there are some other kinds of numbers as 99 or 168.

%H Robert Israel, <a href="/A068422/b068422.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= proc(n) uses numtheory; type(sigma(n)/(n - phi(n)), integer) end proc:

%p select(filter, [$2..1000]); # _Robert Israel_, May 03 2019

%t Select[Range[2,200],Divisible[DivisorSigma[1,#], #-EulerPhi[#]]&]  (* _Harvey P. Dale_, Mar 14 2011 *)

%Y Cf. A000010, A000203, A055164.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Mar 02 2002