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A212953 Minimal order of degree-n irreducible polynomials over GF(2). 3
1, 3, 7, 5, 31, 9, 127, 17, 73, 11, 23, 13, 8191, 43, 151, 257, 131071, 19, 524287, 25, 49, 69, 47, 119, 601, 2731, 262657, 29, 233, 77, 2147483647, 65537, 161, 43691, 71, 37, 223, 174763, 79, 187, 13367, 147, 431, 115, 631, 141, 2351, 97, 4432676798593, 251 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = smallest odd m such that A002326((m-1)/2) = n. - Thomas Ordowski, Feb 04 2014

For n > 1; n < a(n) < 2^n, wherein a(n) = n+1 iff n+1 is A001122 a prime with primitive root 2, or a(n) = 2^n-1 iff n is a Mersenne exponent A000043. - Thomas Ordowski, Feb 08 2014

REFERENCES

W. Narkiewicz, Elementary and Analytic Theory of Algebraic Numbers, Springer 2004, Third Edition, 4.3 Factorization of Prime Ideals in Extensions. More About the Class Group (Theorem 4.33), 4.4 Notes to Chapter 4 (Theorem 4.40). - Regarding the first comment.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..179

Eric Weisstein's World of Mathematics, Irreducible Polynomial

Eric Weisstein's World of Mathematics, Polynomial Order

FORMULA

a(n) = min(M(n)) with M(n) = {d : d|(2^n-1)} \ U(n-1) and U(n) = M(n) union U(n-1) for n>0, U(0) = {}.

a(n) = A059912(n,1) = A213224(n,1).

EXAMPLE

For n=4 the degree-4 irreducible polynomials p over GF(2) are 1+x+x^2+x^3+x^4, 1+x+x^4, 1+x^3+x^4. Their orders (i.e., the smallest integer e for which p divides x^e+1) are 5, 15, 15. (Example: (1+x+x^2+x^3+x^4) * (1+x) == x^5+1 (mod 2)). Thus the minimal order is 5 and a(4) = 5.

MAPLE

with(numtheory):

M:= proc(n) option remember;

      divisors(2^n-1) minus U(n-1)

    end:

U:= proc(n) option remember;

      `if`(n=0, {}, M(n) union U(n-1))

    end:

a:= n-> min(M(n)[]):

seq(a(n), n=1..50);

MATHEMATICA

M[n_] := M[n] = Divisors[2^n-1] ~Complement~ U[n-1];

U[n_] := U[n] = If[n == 0, {}, M[n] ~Union~ U[n-1]];

a[n_] := Min[M[n]];

Array[a, 50] (* Jean-Fran├žois Alcover, Mar 22 2017, translated from Maple *)

CROSSREFS

Cf. A059912, A213224.

Sequence in context: A186522 A048857 A005420 * A161818 A161509 A108974

Adjacent sequences:  A212950 A212951 A212952 * A212954 A212955 A212956

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Jun 01 2012

STATUS

approved

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Last modified December 9 19:51 EST 2019. Contains 329879 sequences. (Running on oeis4.)