A015819 - OEIS

%I #30 Dec 13 2018 12:48:33

%S 3,6,7,11,15,19,21,23,27,31,33,42,43,51,57,59,62,69,70,71,77,79,83,84,

%T 87,93,103,131,139,141,159,163,165,177,187,189,191,199,211,213,223,

%U 235,237,251,267,270,271,282,285,287,297,311,315,316,321,330,331

%N Numbers k such that phi(k + 3) | sigma(k).

%H Vincenzo Librandi, <a href="/A015819/b015819.txt">Table of n, a(n) for n = 1..1000</a>

%p select(t -> (numtheory:-sigma(t)/numtheory:-phi(t+3))::integer, [$1..1000]); # _Robert Israel_, Dec 13 2018

%t Select[Range[1000], Divisible[DivisorSigma[1, #], EulerPhi[3 + #]] &] (* _David Nacin_, Mar 01 2012 *)

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

%Y Cf. A056097.

%Y Contains A092109.

%K nonn

%O 1,1

%A _Robert G. Wilson v_