cp's OEIS Frontend

A118700 Odd n such that 2*phi(n) < n, but there does not exist an even k < n with phi(k) = phi(n).

%I A118700 #11 Aug 16 2012 23:16:24
%S A118700 9075,11985,19965,21165,22515,22815,34935,35445,44505,45315,59415,
%T A118700 67431,67545,108927,135945,143451,180999,286425,295659,359499,360315,
%U A118700 372945,449445,463845,521157,563295,576045,606879,607905,684411,736695,753225,762105,780549,800565
%N A118700 Odd n such that 2*phi(n) < n, but there does not exist an even k < n with phi(k) = phi(n).
%H A118700 Donovan Johnson, <a href="/A118700/b118700.txt">Table of n, a(n) for n = 1..1000</a>
%e A118700 105 is the smallest odd number such that 2*phi(n) < n, but phi(105) = 48 = phi(104), so 105 is not in the sequence.
%o A118700 (PARI) evenphimatch(n)=local(ph,i,r);ph=eulerphi(n);r=0;forstep(i=2*ph,n-1,2,if(eulerphi(i)==ph,r=i;break));r
%o A118700 nextoddlowphi(n)=while(2*eulerphi(n)>n,n+=2);n
%o A118700 i=1;while(i<1000000,i=nextoddlowphi(i+2);if(evenphimatch(i)==0,print(i)))
%Y A118700 Members of A119434 not in A036798.
%K A118700 nonn
%O A118700 1,1
%A A118700 _Franklin T. Adams-Watters_, May 20 2006