A066154 - OEIS

%I #12 Dec 19 2024 21:16:20

%S 574,3496,148708,380276,604504,703402,1223194,1961218,2375854,5153085,

%T 13182476,15089116,15624820,18503524,19402515,22352968,27366118,

%U 41377798,42917332,51062116,58911736,60113914,74657636,75018856

%N Numbers k such that phi(k) = sigma(k) - sigma(k-1).

%H Harry J. Smith, <a href="/A066154/b066154.txt">Table of n, a(n) for n = 1..29</a>

%e phi(574) = 240 = 1008 - 768 = sigma(574) - sigma(573).

%t Select [Range[1, 10^7], EulerPhi[ # ] == DivisorSigma[1, # ] - DivisorSigma[1, # - 1] & ]

%o (PARI) isok(k) = { k > 1 && eulerphi(k) == sigma(k) - sigma(k - 1) } \\ _Harry J. Smith_, Feb 03 2010

%K nonn

%O 1,1

%A _Joseph L. Pe_, Dec 13 2001

%E a(11)-a(24) from _Harry J. Smith_, Feb 03 2010