A163776 -id:A163776 - cp's OEIS frontend

A071642 Numbers n such that x^n + x^(n-1) + x^(n-2) + ... + x + 1 is irreducible over GF(2).

0, 1, 2, 4, 10, 12, 18, 28, 36, 52, 58, 60, 66, 82, 100, 106, 130, 138, 148, 162, 172, 178, 180, 196, 210, 226, 268, 292, 316, 346, 348, 372, 378, 388, 418, 420, 442, 460, 466, 490, 508, 522, 540, 546, 556, 562, 586, 612, 618, 652, 658, 660, 676, 700, 708, 756, 772

Offset: 1

N. J. A. Sloane, Jun 22 2002

All such polynomials of odd degree > 1 are reducible over GF(2).
For n >= 2, a(n) = A001122(n-2) - 1 due to the relationship between cycles and irreducibility. - T. D. Noe, Sep 09 2003
n such that a type-1 optimal normal basis of GF(2^n) (over GF(2)) exists. The corresponding field polynomial is the all-ones polynomial x^n+x^(n-1)+...+1. - Joerg Arndt, Feb 25 2008
From Peter R. J. Asveld, Aug 13 2009: (Start)
a(n) is also the n-th S-prime (Shuffle prime)
For N>=2, the family of shuffle permutations is defined by
p(m,N) = 2m (mod N+1) if N is even,
p(m,N) = 2m (mod N) if N is odd and 1<=mp(N,N) = N if N is odd.
N is S-prime if p(m,N) consists of a single cycle of length N.
So all S-primes are even.
N is S-prime iff p=N+1 is an odd prime number and +2 generates Z_p^* (the multiplicative group of Z_p).
a(n)/2 results in the Josephus_2-primes (A163782). Considered as sets a(n)/2 is the union of A163777 and A163779. If b(n) denotes the dual shuffle primes (A163776), then the union of a(n)/2 and b(n)/2 is equal to the Twist-primes or Queneau numbers (A054639); their intersection is equal to the Archimedes_0-primes (A163777). (End)
Conjecture: Terms >= 2 are numbers n such that P^n + P^(n-1) + P^(n-2) + ... + P + 1 is irreducible over GF(2), where P=x^2+x+1. - Luis H. Gallardo, Dec 23 2019

			For n=4 and n=6 we obtain the permutations (1 2 4 3) and (1 2 4)(3 6 5): 4 is S-prime, but 6 is not. [_Peter R. J. Asveld_, Aug 13 2009]

P. R. J. Asveld, Table of n, a(n) for n = 1..3605
Joerg Arndt, Matters Computational (The Fxtbook), section 42.9 "Gaussian normal bases", pp.914-920
P. R. J. Asveld, Permuting operations on strings and their relation to prime numbers, Discrete Applied Mathematics 159 (2011) 1915-1932.
P. R. J. Asveld, Permuting operations on strings and the distribution of their prime numbers, (2011), TR-CTIT-11-24, Dept. of CS, Twente University of Technology, Enschede, The Netherlands.
P. R. J. Asveld, Some Families of Permutations and Their Primes (2009), TR-CTIT-09-27, Dept. of CS, Twente University of Technology, Enschede, The Netherlands.
P. R. J. Asveld, Permuting Operations on Strings-Their Permutations and Their Primes, Twente University of Technology, 2014.
Hélianthe Caure, Canons rythmiques et pavages modulaires, Thesis Université Pierre et Marie Curie - Paris VI, 2016. See page 108. In French.
H. Caure, C. Agon, and M. Andreatta, Modulus p Rhythmic Tiling Canons and some implementations in Open Music visual programming language, in Proceedings ICMC|SMC|2014 14-20 September 2014, Athens, Greece.
M. Olofsson, VLSI Aspects on Inversion in Finite Fields, Dissertation No. 731, Dept. Elect. Engin., Linkoping, Sweden, 2002.
Eric Weisstein's World of Mathematics, Irreducible Polynomial
Index entries for sequences related to the Josephus Problem

Cf. A001122 (primes with primitive root 2).

Join[{0, 1}, Reap[For[p = 2, p < 10^3, p = NextPrime[p], If[ MultiplicativeOrder[2, p] == p-1, Sow[p-1]]]][[2, 1]]] (* Jean-François Alcover, Dec 10 2015, adapted from PARI *)

forprime(p=3,1000,if(znorder(Mod(2,p))==p-1,print1(p-1,", "))) /* Joerg Arndt, Jul 05 2011 */

Extended by Robert G. Wilson v, Jun 24 2002

Initial terms of b-file corrected by N. J. A. Sloane, Aug 31 2009

A054639 Queneau numbers: numbers n such that the Queneau-Daniel permutation {1, 2, 3, ..., n} -> {n, 1, n-1, 2, n-2, 3, ...} is of order n.

Original entry on oeis.org

1, 2, 3, 5, 6, 9, 11, 14, 18, 23, 26, 29, 30, 33, 35, 39, 41, 50, 51, 53, 65, 69, 74, 81, 83, 86, 89, 90, 95, 98, 99, 105, 113, 119, 131, 134, 135, 146, 155, 158, 173, 174, 179, 183, 186, 189, 191, 194, 209, 210, 221, 230, 231, 233, 239

Offset: 1

Gilles Esposito-Farese (gef(AT)cpt.univ-mrs.fr), May 17 2000

nonn

The troubadour Arnaut Daniel composed sestinas based on the permutation 123456 -> 615243, which cycles after 6 iterations.
Roubaud quotes the number 141, but the corresponding Queneau-Daniel permutation is only of order 47 = 141/3.
This appears to coincide with the numbers n such that a type-2 optimal normal basis exists for GF(2^n) over GF(2). But are these two sequences really the same? - Joerg Arndt, Feb 11 2008
The answer is Yes - see Theorem 2 of the Dumas reference. [Jean-Guillaume Dumas (Jean-Guillaume.Dumas(AT)imag.fr), Mar 20 2008]
From Peter R. J. Asveld, Aug 17 2009: (Start)
a(n) is the n-th T-prime (Twist prime). For N >= 2, the family of twist permutations is defined by
p(m,N) == +2m (mod 2N+1) if 1 <= m < k = ceiling((N+1)/2),
p(m,N) == -2m (mod 2N+1) if k <= m < N.
N is T-prime if p(m,N) consists of a single cycle of length N.
The twist permutation is the inverse of the Queneau-Daniel permutation.
N is T-prime iff p=2N+1 is a prime number and exactly one of the following three conditions holds;
(1) N == 1 (mod 4) and +2 generates Z_p^* (the multiplicative group of Z_p) but -2 does not,
(2) N == 2 (mod 4) and both +2 and -2 generate Z_p^*,
(3) N == 3 (mod 4) and -2 generate Z_p^* but +2 does not. (End)
The sequence name says the permutation is of order n, but P. R. J. Asveld's comment says it's an n-cycle. Is there a proof that those conditions are equivalent for the Queneau-Daniel permutation? (They are not equivalent for any arbitrary permutation; e.g., (123)(45)(6) has order 6 but isn't a 6-cycle.) More generally, I have found that for all n <= 9450, (order of Queneau-Daniel permutation) = (length of orbit of 1) = A003558(n). Does this hold for all n? - David Wasserman, Aug 30 2011

			For N=6 and N=7 we obtain the permutations (1 2 4 5 3 6) and (1 2 4 7)(3 6)(5): 6 is T-prime, but 7 is not. - _Peter R. J. Asveld_, Aug 17 2009

Raymond Queneau, Note complémentaire sur la Sextaine, Subsidia Pataphysica 1 (1963), pp. 79-80.
Jacques Roubaud, Bibliothèque Oulipienne No 65 (1992) and 66 (1993).

P. R. J. Asveld, Table of n, a(n) for n = 1..10085
Jean-Paul Allouche, Manon Stipulanti, and Jia-Yan Yao, Doubling modulo odd integers, generalizations, and unexpected occurrences, arXiv:2504.17564 [math.NT], 2025.
Joerg Arndt, Matters Computational (The Fxtbook), section 42.9 "Gaussian normal bases", pp. 914-920
P. R. J. Asveld, Permuting operations on strings and their relation to prime numbers, Discrete Applied Mathematics 159 (2011) 1915-1932.
P. R. J. Asveld, Permuting operations on strings and the distribution of their prime numbers, TR-CTIT-11-24, Dept. of CS, Twente University of Technology, Enschede, The Netherlands.
P. R. J. Asveld, Some families of permutations and their primes (2009), TR-CTIT-09-27, Dept. of CS, Twente University of Technology, Enschede, The Netherlands.
P. R. J. Asveld, Queneau Numbers--Recent Results and a Bibliography, University of Twente, 2013.
P. R. J. Asveld, Permuting Operations on Strings-Their Permutations and Their Primes, Twente University of Technology, 2014.
Michèle Audin, Poésie, Spirales, et Battements de Cartes, Images des Mathématiques, CNRS, 2019 (in French).
M. Bringer, Sur un problème de R. Queneau, Math. Sci. Humaines No. 25 (1969) 13-20.
Jean-Guillaume Dumas, Caractérisation des Quenines et leur représentation spirale, Mathématiques et Sciences Humaines, Centre de Mathématique Sociale et de statistique, EPHE, 2008, 184 (4), pp. 9-23, hal-00188240.
G. Esposito-Farese, C program
Index entries for sequences related to the Josephus Problem

Not to be confused with Queneau's "s-additive sequences", see A003044.
A005384 is a subsequence.
Union of A163782 (Josephus_2-primes) and A163781 (dual Josephus_2-primes); also the union of A163777 (Archimedes_0-primes) and A163778 (Archimedes_1-primes); also the union of A071642/2 (shuffle primes) and A163776/2 (dual shuffle primes). - Peter R. J. Asveld, Aug 17 2009
Cf. A216371, A003558 (for which a(n) == n).

QD:= proc(n) local i;
  if n::even then map(op,[seq([n-i,i+1],i=0..n/2-1)])
  else map(op, [seq([n-i,i+1],i=0..(n-1)/2-1),[(n+1)/2]])
  fi
end proc:
select(n -> GroupTheory:-PermOrder(Perm(QD(n)))=n, [$1..1000]); # Robert Israel, May 01 2016

a[p_] := Sum[Cos[2^n Pi/((2 p + 1) )], {n, 1, p}];
Select[Range[500],Reduce[a[#] == -1/2, Rationals] &] (* Gerry Martens, May 01 2016 *)

is(n)=
{
    if (n==1, return(1));
    my( m=n%4 );
    if ( m==4, return(0) );
    my(p=2*n+1, r=znorder(Mod(2,p)));
    if ( !isprime(p), return(0) );
    if ( m==3 && r==n, return(1) );
    if ( r==2*n, return(1) ); \\ r == 1 or 2
    return(0);
}
for(n=1,10^3, if(is(n),print1(n,", ")) );
\\ Joerg Arndt, May 02 2016

a(n) = (A216371(n)-1)/2. - L. Edson Jeffery, Dec 18 2012

a(n) >> n log n, and on the Bateman-Horn-Stemmler conjecture a(n) << n log^2 n. I imagine a(n) ≍ n log n, and numerics suggest that perhaps a(n) ~ kn log n for some constant k (which seems to be around 1.122). - Charles R Greathouse IV, Aug 02 2023

A323712 Number of the following described shuffles required to return a deck of n cards to its original state. Create two piles by alternating a card from the top of the deck left-right-left-right until the deck is exhausted. Then, placing the left pile on top of the right pile constitutes one shuffle.

Original entry on oeis.org

1, 1, 3, 4, 4, 6, 6, 3, 9, 5, 5, 12, 12, 4, 12, 8, 8, 9, 9, 6, 6, 22, 22, 20, 20, 9, 27, 28, 28, 10, 10, 5, 15, 12, 12, 36, 36, 12, 12, 20, 20, 7, 7, 12, 36, 46, 46, 42, 42, 8, 24, 52, 52, 20, 20, 9, 9, 29, 29, 60, 60, 6, 18, 12, 12, 33, 33, 22, 66, 70, 70, 18

Offset: 1

David Lovler, Jan 24 2019

nonn

The card shuffling procedure is the same for even n and odd n.
Here are a few conjectures.
a(n) <= n for all n.
a(p)=a(p-1) and a(p)|p-1 when p is a prime >= 5.
a(n)=a(n-1) and a(n)|n-1 for nonprimes 341=31*11 and 22369621=8191*2731 and probably other pseudoprimes of the form p*((p+2)/3) where p is a Mersenne prime and (p+2)/3 is prime.
n cards are returned to their original state after n shuffles when n=1, 3, 4, 6, 9, 12, 22, 27, 28, 36, 46, 52, 60, 70, 78, 81, ... (A373461) . These values of n are either of the form p-1 where p is an odd prime number or 3^i, i >= 0.
a(c) is relatively small (compared with nearby values) when c is a Catalan number.
a(2n+1)=3*a(2n) or a(2n+1)=a(2n) for all n.

			For n=4, {a1,a2,a3,a4}-->{a3,a1,a4,a2}-->{a4,a3,a2,a1}-->{a2,a4,a1,a3}-->{a1,a2,a3,a4}, so a(4)=4.
For n=5, {a1,a2,a3,a4,a5}-->{a5,a3,a1,a4,a2}-->{a2,a1,a5,a4,a3}-->{a3,a5,a2,a4,a1}-->{a1,a2,a3,a4,a5}, so a(5)=4.

Alois P. Heinz, Table of n, a(n) for n = 1..1024

Cf. A024222, A022998, A163776, A373416 (fixed points).

pileShuf := proc(L::list)
    local i,n,shf ;
    shf := [] ;
    n := nops(L) ;
    if type(n,'odd') then
        for i from n to 1 by -2 do
            shf := [op(shf),op(i,L)] ;
        end do:
        for i from n-1 to 2 by -2 do
            shf := [op(shf),op(i,L)] ;
        end do:
    else
        for i from n-1 to 1 by -2 do
            shf := [op(shf),op(i,L)] ;
        end do:
        for i from n to 2 by -2 do
            shf := [op(shf),op(i,L)] ;
        end do:
    end if;
    shf ;
end proc:
A323712 := proc(n)
    local L,itr,isord,i;
    L := [seq(i,i=1..n)] ;
    for itr from 1 to n! do
        L := pileShuf(L) ;
        isord := true ;
        for i from 1 to nops(L) do
            if op(i,L) <> i then
                isord := false ;
                break ;
            end if;
        end do:
        if isord then
            return itr ;
        end if;
    end do:
    -1 ;
end proc:
seq(A323712(n),n=1..50) ; # R. J. Mathar, Aug 02 2024

perm(n, vn) = {my(va = List(), vb = List()); for (k=1, n, if (k % 2, listput(va, vn[k]), listput(vb, vn[k]));); Vec(concat(Vecrev(va), Vecrev(vb)));}
a(n) = {my(vn = vector(n,k,k), vs = perm(n, vn), nb = 1); while (vs != vn, vs = perm(n, vs); nb++); nb;} \\ Michel Marcus, Feb 06 2019

a(2^m) = m if m is odd, a(2^m) = 2m if m is even. - Alois P. Heinz, Feb 15 2019

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cp's OEIS Frontend

A071642 Numbers n such that x^n + x^(n-1) + x^(n-2) + ... + x + 1 is irreducible over GF(2).

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A054639 Queneau numbers: numbers n such that the Queneau-Daniel permutation {1, 2, 3, ..., n} -> {n, 1, n-1, 2, n-2, 3, ...} is of order n.

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