A217460 Odd values of n such that the polynomial 1+x+x^2+...+x^(n-1) is reducible over GF(2).

7, 9, 15, 17, 21, 23, 25, 27, 31, 33, 35, 39, 41, 43, 45, 47, 49, 51, 55, 57, 63, 65, 69, 71, 73, 75, 77, 79, 81, 85, 87, 89, 91, 93, 95, 97, 99, 103, 105, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129, 133, 135, 137, 141, 143, 145, 147, 151, 153, 155, 157, 159, 161, 165, 167, 169, 171, 175, 177, 183, 185, 187, 189, 191, 193, 195, 199

Offset

1,1

Comments

This sequence is the union of the odd composite numbers and the primes for which 2 is not a primitive root.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Mathematica

nn = 200; Union[Select[Range[3, nn, 2], ! PrimeQ[#] &], Select[Prime[Range[2, PrimePi[nn]]], PrimitiveRoot[#] =!= 2 &]] (* T. D. Noe, Sep 19 2012 *)

Prog

(PARI) for(i=4, 200, if(isprime(i), if(znorder(Mod(2, i))!=(i-1), print(i)), if(i%2==1, print(i))))
(PARI)  for(i=0, 200, i++; if(matsize(factormod((x^i+1)/(x+1), 2, 1))[1]>1, print(i)))

Crossrefs

Cf. A002326, A001122, A216838.

Sequence in context: A282758 A073457 A067873 * A347436 A047522 A112072

Adjacent sequences: A217457 A217458 A217459 * A217461 A217462 A217463

Keyword

nonn

Author

V. Raman, Oct 04 2012

Status

approved