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A118700

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

9075, 11985, 19965, 21165, 22515, 22815, 34935, 35445, 44505, 45315, 59415, 67431, 67545, 108927, 135945, 143451, 180999, 286425, 295659, 359499, 360315, 372945, 449445, 463845, 521157, 563295, 576045, 606879, 607905, 684411, 736695, 753225, 762105, 780549, 800565

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OFFSET

1,1

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..1000

EXAMPLE

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.

PROG

(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

nextoddlowphi(n)=while(2*eulerphi(n)>n, n+=2); n

i=1; while(i<1000000, i=nextoddlowphi(i+2); if(evenphimatch(i)==0, print(i)))

CROSSREFS