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%I #36 Dec 07 2012 15:21:57
%S 3,4,5,6,8,9,10,11,12,13,14,15,16,18,19,20,21,22,24,25,26,27,28,29,30,
%T 32,33,34,35,36,37,38,39,40,42,44,45,46,48,49,50,51,52,53,54,55,56,57,
%U 58,59,60,61,62,63,64,65,66,67,68,69,70,72,74,75,76,77,78
%N Union of the composite numbers and the primes for which 2 is a primitive root.
%C This is the complement of A216838 (primes for which 2 is not a primitive root). [_V. Raman_, Dec 01 2012]
%t nn = 100; Union[Select[Range[2, nn], ! PrimeQ[#] &], Select[Prime[Range[2, PrimePi[nn]]], PrimitiveRoot[#] == 2 &]] (* _T. D. Noe_, Sep 19 2012 *)
%o (PARI) for(i=1, 100, if(isprime(i), if(znorder(Mod(2, i))!=(i-1), print1(i, ", ")), print1(i, ", "))); /* _V. Raman_, Sep 17 2012 */
%o (PARI)
%o is_A216846(n) = if( !isprime(n), 1, if(znorder(Mod(2,n))==n-1, 1, 0) );
%o for(n=3,100,if(is_A216846(n),print1(n,", ")));
%o /* _Joerg Arndt_, Oct 15 2012 */
%Y Cf. A002326, A001122, A216838.
%K nonn
%O 1,1
%A _V. Raman_, Sep 17 2012
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