%I #26 Aug 13 2021 19:17:19

%S 1,2,12,42,1242,75960,1447488,3506976,6137440,10834488,17156160,

%T 90288000,431440416,454460160,704592000,1385119360,1588268480,

%U 10674673152,24913095480,31103703540,56015374080,80767843200,129631788000,463308768000,469897798656,834460413696

%N Numbers k that divide sigma(k)-phi(k).

%C a(37) > 10^13. - _Giovanni Resta_, Jun 12 2013

%H Giovanni Resta, <a href="/A055681/b055681.txt">Table of n, a(n) for n = 1..36</a> (terms < 10^13)

%p with(numtheory): A055681:=n->`if`(sigma(n)-phi(n) mod n=0,n,NULL): seq(A055681(n), n=1..10^5); # _Wesley Ivan Hurt_, Sep 13 2014

%t Do[If[Mod[DivisorSigma[1, n]-EulerPhi[n], n]==0, Print[n]], {n, 1, 10^9}]

%o (PARI)

%o for(n=1,10^8,if((sigma(n)-eulerphi(n))%n==0,print1(n,", "))) \\ _Derek Orr_, Sep 13 2014

%Y Cf. A011774, A000203, A000010, A054024, A056075.

%K nonn

%O 1,2

%A _Robert G. Wilson v_, Jun 09 2000

%E a(16)-a(26) from _Donovan Johnson_, Feb 28 2012