A066694 - OEIS

%I #19 Sep 10 2024 08:44:30

%S 4,9,16,18,25,32,36,48,50,64,72,81,84,98,100,112,144,156,162,192,196,

%T 200,225,252,256,288,289,300,324,336,338,372,392,400,432,448,450,468,

%U 484,512,576,578,624,625,648,676,700,722,729,756,768,784,800,882,900

%N Numbers k such that phi(sigma(k)) > k.

%H Harry J. Smith, <a href="/A066694/b066694.txt">Table of n, a(n) for n = 1..1000</a>

%H Amiram Eldar, <a href="/A066694/a066694.jpg">Plot of a(n)/(n*log(n)^2) for n = 2^(4..21)</a>.

%F It seems that a(n) is asymptotic to C*n*log(n)^2 with C=1.38.... - _Benoit Cloitre_, Aug 07 2002

%t Select[Range[1, 10^3], EulerPhi[DivisorSigma[1, # ]] > # &]

%o (PARI) { n=0; for (m=1, 10^10, if (eulerphi(sigma(m)) > m, write("b066694.txt", n++, " ", m); if (n==1000, return)) ) } \\ _Harry J. Smith_, Mar 18 2010

%Y Cf. A000010, A000203, A001229, A062401, A295307.

%K easy,nonn

%O 1,1

%A _Joseph L. Pe_, Jan 09 2002

%E More terms from _Benoit Cloitre_, Jul 31 2002