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A216838 Odd primes for which 2 is not a primitive root. 12
7, 17, 23, 31, 41, 43, 47, 71, 73, 79, 89, 97, 103, 109, 113, 127, 137, 151, 157, 167, 191, 193, 199, 223, 229, 233, 239, 241, 251, 257, 263, 271, 277, 281, 283, 307, 311, 313, 331, 337, 353, 359, 367, 383, 397, 401, 409, 431, 433, 439, 449, 457, 463, 479 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Alternately, for these primes p, the polynomial (x^p+1)/(x+1) is reducible over GF(2).

The prime p belongs to this sequence if and only if A002326((p-1)/2) != (p-1). If A002326((p-1)/2) = (p-1), then the prime p belongs to the sequence A001122. - V. Raman, Dec 01 2012

The only primitive root modulo 2 is 1. See A060749. Hence 2 should be added to this sequence in order to obtain the complement of A001122. - Wolfdieter Lang, May 19 2014

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

select(t -> isprime(t) and numtheory[order](2, t) <> t-1, [seq](2*i+1, i=1..1000)); # Robert Israel, May 20 2014

MATHEMATICA

Select[Prime[Range[2, 100]], PrimitiveRoot[#] =!= 2 &] (* T. D. Noe, Sep 19 2012 *)

PROG

(PARI) forprime(p=3, 1000, if(znorder(Mod(2, p))!=p-1, print(p)))

(PARI) forprime(p=3, 1000, if(factormod((x^p+1)/(x+1), 2, 1)[1, 1]!=(p-1), print(p)))

CROSSREFS

Cf. A002326 (multiplicative order of 2 mod 2n+1)

Cf. A001122 (Primes for which 2 is a primitive root).

Sequence in context: A107643 A289363 A319040 * A198441 A058529 A253408

Adjacent sequences:  A216835 A216836 A216837 * A216839 A216840 A216841

KEYWORD

nonn

AUTHOR

V. Raman, Sep 17 2012

EXTENSIONS

Name corrected by Wolfdieter Lang, May 19 2014

STATUS

approved

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Last modified July 8 00:31 EDT 2020. Contains 335502 sequences. (Running on oeis4.)