login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A057496 Numbers n such that x^n + x^3 + x^2 + x + 1 is irreducible over GF(2). 0
1, 2, 3, 4, 5, 7, 10, 17, 20, 25, 28, 31, 41, 52, 130, 151, 196, 503, 650, 761, 986, 1391, 2047, 6172, 6431, 6730, 8425, 10162, 11410, 12071, 13151, 14636, 17377, 18023, 32770, 77047, 102842, 130777, 137113, 143503, 168812, 192076 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

If x^n + x^3 + x^2 + x + 1 is irreducible, then so is its "twin" x^n + x^3 + 1. - Gove Effinger, Mar 11 2007

LINKS

Table of n, a(n) for n=1..42.

FORMULA

Using probabilistic arguments it appears that there should be about 6.5 terms in this sequence with any given number of decimal digits d. - Gove Effinger, Mar 11 2007

MATHEMATICA

Do[ If[ ToString[ Factor[ x^n + x^3 + x^2 + x + 1, Modulus -> 2 ] ] == ToString[ x^n + x^3 + x^2 + x + 1 ], Print[ n ] ], {n, 0, 750} ]

CROSSREFS

Sequence in context: A282502 A212463 A130080 * A191864 A180348 A001729

Adjacent sequences:  A057493 A057494 A057495 * A057497 A057498 A057499

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Sep 27 2000

EXTENSIONS

a(20) - a(23) from Robert G. Wilson v, Mar 11 2007

a(24) - a(27) computed by Richard P. Brent, Mar 11 2007, communicated by Gove Effinger

a(27) - a(35) computed by Richard P. Brent, Mar 16 2007, communicated by Gove Effinger

a(36) - a(42) computed by Jonathan Webster, Feb 18 2010

Added entries a(1), a(2), a(3) since x^3 + x^2 + 1, x^3 + x + 1 and x^2 + x + 1 are irreducible over GF(2). Changed the offset for the entries computed by Robert G. Wilson v and Richard P. Brent to account for this. Added terms a(36) through a(42). - Jonathan Webster (jwebster(AT)bates.edu), Feb 18 2010

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 15 07:34 EDT 2018. Contains 316203 sequences. (Running on oeis4.)