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 A070170 Numbers n such that sigma(n-phi(n)) = phi(n). 2

%I

%S 2,15,39,255,627,939,1431,1581,2409,3459,4797,14289,20619,30987,31935,

%T 43791,57291,68991,71193,73749,74841,94671,120669,121227,132297,

%U 148161,162843,196449,200787,209451,217191,302907,308937,434733,439959,455961,466701,467109

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

%C All terms 2 < a(n) < 20000000 are odd and divisible by 3. Most are squarefree.

%C From numerical observation if n>31 : log(n)^10 < a(n) < log(n)^11.

%H Donovan Johnson, <a href="/A070170/b070170.txt">Table of n, a(n) for n = 1..500</a>

%t Do[s=DivisorSigma[1, (n-EulerPhi[n])]-EulerPhi[n]; If[Equal[s, 0], Print[n]], {n, 1, 2000000}]

%o (PARI) for(n=2, 2000000, if(sigma(n-eulerphi(n))==eulerphi(n), print1(n, ", ")))

%Y Cf. A070171.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_ and _Labos Elemer_, May 06 2002

%E Edited by _Charles R Greathouse IV_, Oct 28 2009

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Last modified May 18 12:26 EDT 2021. Contains 343995 sequences. (Running on oeis4.)