A070738 - OEIS

%I #7 Feb 07 2016 11:27:12

%S 1,4,8,16,18,28,30,32,36,50,54,56,64,72,75,100,102,104,108,128,144,

%T 162,200,204,208,216,234,245,250,256,288,294,306,324,400,405,408,432,

%U 486,500,512,567,576,588,612,648,693,800,864,882,900,972,990,1000,1024

%N Nonprimes n such that n^2 reduced modulo phi(n) = phi(n)^2 reduced modulo n.

%C All powers of 2 are in the sequence.

%H Harvey P. Dale, <a href="/A070738/b070738.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[1100],!PrimeQ[#]&&PowerMod[#,2,EulerPhi[#]]== PowerMod[ EulerPhi[ #],2,#]&] (* _Harvey P. Dale_, Feb 07 2016 *)

%o (PARI) for(n=1,2000,if(n^2%eulerphi(n)*(-1)^isprime(n)==eulerphi(n)^2%n,print1(n,",")))

%K easy,nonn

%O 1,2

%A _Benoit Cloitre_, May 14 2002