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Numbers k such that phi(k) | sigma(k + 2).
6

%I #21 Sep 09 2019 01:23:31

%S 1,2,3,4,5,9,10,12,13,18,21,22,25,28,36,38,40,42,45,52,55,58,60,90,93,

%T 108,112,117,130,152,153,156,175,180,182,187,208,222,226,228,246,258,

%U 264,280,306,310,313,380,396,468,490,504,532,592,609,628,700,715

%N Numbers k such that phi(k) | sigma(k + 2).

%H Ivan Neretin, <a href="/A015837/b015837.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[3000], Divisible[DivisorSigma[1, 2 + #], EulerPhi[#]] &] (* _David Nacin_, Mar 03 2012 *)

%o (PARI) isok(n) = !(sigma(n+2) % eulerphi(n)); \\ _Michel Marcus_, Feb 05 2017

%K nonn

%O 1,2

%A _Robert G. Wilson v_

%E a(1) = 1 inserted by _Ivan Neretin_, Feb 05 2017