A078752 - OEIS

%I #8 Nov 21 2013 12:47:56

%S 3,3,5,5,11,7,13,11,13,11,23,13,29,17,17,17,37,19,37,23,29,23,47,25,

%T 41,29,37,29,59,31,61,37,41,37,53,37,73,41,53,41,83,43,89,47,53,47,97,

%U 49,89,53,67,53,107,55,83,59,73,59,127,61,127,67,73,67,97,67,137,71,89,71

%N Least m>n such that phi(m) >= 2*phi(n), where phi is Euler's totient function (A000010).

%C For odd primes p: a(p-1) = p; the converse is not true, as e.g. a(25-1)=25.

%H Harvey P. Dale, <a href="/A078752/b078752.txt">Table of n, a(n) for n = 1..1000</a>

%t epm[n_]:=Module[{m=n+1,epn2=2EulerPhi[n]},While[EulerPhi[m]<epn2, m++];m]; Array[epm, 70] (* _Harvey P. Dale_, Apr 13 2012 *)

%o (PARI) a(n)=my(t=2*eulerphi(n),m=max(n,t));while(eulerphi(m++)<t,); m \\ _Charles R Greathouse IV_, Feb 21 2013

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Dec 22 2002