A039786 - OEIS

%I #6 Mar 11 2014 22:22:58

%S 2,3,5,7,9,11,13,23,29,31,43,47,53,59,61,67,71,79,83,103,107,131,139,

%T 149,157,167,173,179,191,211,223,227,229,239,263,269,277,283,293,311,

%U 317,331,347,349,359,367,373,383,389,419,421,431,439,443,461,463,467,479

%N phi(a(n)) is equal to the multiplicative projection of (a(n)-1).

%C Only primes (except 9) may qualify.

%H Charles R Greathouse IV, <a href="/A039786/b039786.txt">Table of n, a(n) for n = 1..10000</a>

%e phi(29)=28, 28=2^2*7^1, 2*2*7*1=28.

%o (PARI) is(n)=my(f=factor(n)); eulerphi(f)==prod(i=1,#f~,f[i,1]*f[i,2])-1 \\ _Charles R Greathouse IV_, Mar 11 2014

%Y Cf. A000010, A000026.

%K nonn

%O 1,1

%A _Olivier Gérard_

%E a(1) inserted by _Charles R Greathouse IV_, Mar 11 2014