A073543 - OEIS

%I #17 Feb 20 2021 23:10:42

%S 12,36,37,72,73,86,95,181,192,482,540,541,560,637,813,1152,1620,1621,

%T 1683,2017,2101,2283,2557,2592,2642,2916,3031,3032,3061,3381,3624,

%U 3625,4357,5077,5186,5581,6337,6661,7417,8100,9118,9181,9299,9720,9901

%N Numbers k such that 1/(1/phi(k) + 1/phi(k+1) + 1/phi(k+2)) is an integer.

%H Seiichi Manyama, <a href="/A073543/b073543.txt">Table of n, a(n) for n = 1..10000</a>

%e 1/phi(2283)+1/phi(2284)+1/phi(2285) = 1/1520+1/1140+1/1824 = 1/480 so 2283 is in the sequence.

%t Select[Range[10000], IntegerQ[1/Sum[1/EulerPhi[ #+i], {i, 0, 2}]]&]

%o (PARI) isok(k) = numerator(1/eulerphi(k) + 1/eulerphi(k+1) + 1/eulerphi(k+2)) == 1; \\ _Michel Marcus_, Feb 18 2021

%Y Cf. A000010, A073542, A073544, A341745, A341799.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Aug 27 2002

%E Edited by _Dean Hickerson_, Sep 03 2002