cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-10 of 10 results.

A074744 Values of k corresponding to A073726.

Original entry on oeis.org

1, 1, 1, 2, 1, 1, 4, 3, 2, 1, 3, 7, 3, 2, 1, 5, 3, 3, 2, 3, 13, 2, 11, 4, 3, 5, 9, 3, 24, 7, 19, 1, 1, 18, 9, 6, 25, 9, 4, 13, 13, 38, 2, 21, 11, 6, 11, 37, 9, 16, 15, 31, 10, 9, 33, 8, 18, 2, 37, 1, 5, 3, 29, 57, 11, 21, 29, 21, 52, 27, 53
Offset: 1

Views

Author

N. J. A. Sloane, Sep 06 2002

Keywords

Comments

If there is more than one choice for k then the smallest value is taken.

Programs

  • Mathematica
    f[n_] := For[k = 1, k <= n - 1, k++, If[PrimitivePolynomialQ[x^n + x^k + 1, 2], Print[k]; Return[k]]];
    DeleteCases[f /@ Range[201], Null] (* Jean-François Alcover, Aug 19 2019 *)

Extensions

a(12) - a(71) from Nathaniel Johnston, Apr 26 2011

A186440 Number of prime divisors (counted with multiplicity) of n such that the primitive irreducible trinomial x^n + x^k + 1 is a primitive irreducible polynomial (mod 2) for some k with 0 < k < n (A073726).

Original entry on oeis.org

1, 1, 2, 1, 2, 1, 2, 2, 1, 2, 1, 3, 3, 2, 2, 1, 2, 3, 1, 1, 2, 2, 4, 2, 1, 1, 2, 3, 2, 2, 2, 4, 3, 2, 3, 1, 1, 1, 4, 4, 2, 1, 2, 2, 2, 1, 3, 4, 1, 3, 2, 5, 2, 1, 2, 2, 2, 2, 3, 1, 2, 3, 4, 2, 4, 1, 4, 2, 2, 3, 4, 1, 3, 2, 2, 1, 2, 3
Offset: 1

Views

Author

Jonathan Vos Post, Feb 21 2011

Keywords

Examples

			a(48) = 4 because A073726(48) = 100, and Omega(100 = 2^2 * 5^2) = 4.
		

Crossrefs

Cf. A001222, A073726, See A074744 for corresponding values of k.

Formula

a(n) = bigomega(A073726(n)) = Omega(A073726(n)) = A001222(A073726(n)).

Extensions

a(49) - a(78) from Nathaniel Johnston, Apr 26 2011

A073571 Irreducible trinomials: numbers n such that x^n + x^k + 1 is an irreducible polynomial (mod 2) for some k with 0 < k < n.

Original entry on oeis.org

2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 14, 15, 17, 18, 20, 21, 22, 23, 25, 28, 29, 30, 31, 33, 34, 35, 36, 39, 41, 42, 44, 46, 47, 49, 52, 54, 55, 57, 58, 60, 62, 63, 65, 66, 68, 71, 73, 74, 76, 79, 81, 84, 86, 87, 89, 90, 92, 93, 94, 95, 97, 98, 100, 102, 103, 105, 106, 108, 110, 111, 113
Offset: 1

Views

Author

Paul Zimmermann, Sep 05 2002

Keywords

Comments

This sequence is infinite: Golomb, "Shift Register Sequences," on p. 96 (1st ed., 1966) states that "It is easy to exhibit an infinite class of irreducible trinomials. viz. x^(2*3^a) + x^(3^a) + 1 for all a = 0, 1, 2, ..., but whose roots have only 3^(a+1) as their period." - A. M. Odlyzko, Dec 05 1997.

References

  • S. W. Golomb, "Shift register sequence", revised edition, reprinted by Aegean Park Press, 1982. See Tables V-1, V-2.

Crossrefs

For the numbers of such trinomials for a given n, see A057646.
See A073726 for primitive trinomials and A001153 for primitive Mersenne trinomials (and references). Complement of A057486. For values of k see A057774.

Programs

  • Maple
    a := proc(n) local k; for k from 1 to n-1 do if Irreduc(x^n+x^k+1) mod 2 then RETURN(n) fi od; NULL end: [seq(a(n), n=1..130)];
  • Mathematica
    irreducibleQ[n_] := (irr = False; k = 1; While[k < n, If[ Factor[ x^n + x^k + 1, Modulus -> 2] == x^n + x^k + 1, irr = True; Break[]]; k++]; irr); Select[ Range[120], irreducibleQ] (* Jean-François Alcover, Jan 07 2013 *)
  • PARI
    is(n)=for(s=1,n-1,if(polisirreducible((x^n+x^s+1)*Mod(1,2)), return(1)));0 \\ Charles R Greathouse IV, May 30 2013

A001153 Degrees of primitive irreducible trinomials: n such that 2^n - 1 is a Mersenne prime and x^n + x^k + 1 is a primitive irreducible polynomial over GF(2) for some k with 0 < k < n.

Original entry on oeis.org

2, 3, 5, 7, 17, 31, 89, 127, 521, 607, 1279, 2281, 3217, 4423, 9689, 19937, 23209, 44497, 110503, 132049, 756839, 859433, 3021377, 6972593, 24036583, 25964951, 30402457, 32582657, 42643801, 43112609
Offset: 1

Views

Author

Keywords

Comments

Also the list of "irreducible Mersenne trinomials" since here irreducible implies primitive.
Further terms of the form +-3 (mod 8) are unlikely, as the only possibility of an irreducible trinomial for n == +-3 (mod 8) is (by Swan's theorem) x^n+x^2+1 (and its reciprocal); see the Ciet et al. and the Swan reference. - Joerg Arndt, Jan 06 2014
The first Mersenne prime exponent not ruled out by Swan's theorem and yet not a member of this sequence is 57885161. - Gord Palameta, Jul 20 2018
74207281 is also in the sequence. - Gord Palameta, Jul 20 2018

References

  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

For smallest values of k, see A074743.

Extensions

Corrected and extended by Paul Zimmermann, Sep 05 2002
Six more terms from Brent's page added by Max Alekseyev, Oct 22 2011

A132454 First primitive GF(2)[X] polynomials of degree n and minimal number of terms, expressed as -k for X^n+X^k+1, else with X^n suppressed.

Original entry on oeis.org

1, -1, -1, -1, -2, -1, -1, 29, -4, -3, -2, 83, 27, 43, -1, 45, -3, -7, 39, -3, -2, -1, -5, 27, -3, 71, 39, -3, -2, 83, -3, 197, -13, 281, -2, -11, 83
Offset: 1

Views

Author

Francois R. Grieu, Aug 22 2007

Keywords

Comments

More precisely: when there exists k, 0

Examples

			a(10)=-3, representing the GF(2)[X] polynomial X^10+X^3+1, because this degree 10 trinomial is primitive, contrary to X^10+X^1+1, X^10+X^2+1 and X^10+X^2+X^1.
		

Crossrefs

Either of 2^n+2^(-a(n))+1 or 2^n+a(n) belongs to A091250. If there exists m such that n = A073726(m), then a(n) = -A074744(m); otherwise a(n) = A132450(n). A132453(n) gives the primitive polynomial corresponding to a(n). Cf. A132448, similar, with no restriction on number of terms. Cf. A132450, similar, with restriction to at most 5 terms. Cf. A132452, similar, with restriction to exactly 5 terms.

A278572 Irregular triangle read by rows: row n lists values of k in range 1 <= k <= n/2 such x^n + x^k + 1 is irreducible (mod 2), or -1 if no such k exists.

Original entry on oeis.org

1, 1, 1, 2, 1, 3, 1, 3, -1, 1, 4, 3, 2, 3, 5, -1, 5, 1, 4, 7, -1, 3, 5, 6, 3, 7, 9, -1, 3, 5, 2, 7, 1, 5, 9, -1, 3, 7, -1, -1, 1, 3, 9, 13, 2, 1, 9, 3, 6, 7, 13, -1, 10, 13, 7, 2, 9, 11, 15, -1, -1, 4, 8, 14, -1, 3, 20, 7, -1, 5, -1, 1, 5, 14, 20, 21, -1
Offset: 2

Author

N. J. A. Sloane, Nov 27 2016

Keywords

Comments

This is the format used by John Brillhart (1968) and Zierler and Brillhart (1968).

Examples

			Triangle begins:
1,
1,
1,
2,
1, 3,
1, 3,
-1,
1, 4,
3,
2,
3, 5,
-1,
5,
1, 4, 7,
-1,
3, 5, 6,
...
		

References

  • Alanen, J. D., and Donald E. Knuth. "Tables of finite fields." Sankhyā: The Indian Journal of Statistics, Series A (1964): 305-328.
  • John Brillhart, On primitive trinomials (mod 2), unpublished Bell Labs Memorandum, 1968.
  • Marsh, Richard W. Table of irreducible polynomials over GF (2) through degree 19. Office of Technical Services, US Department of Commerce, 1957.

Crossrefs

Rows n that contain particular numbers: 1 (A002475), 2 (A057460), 3 (A057461), 4 (A057463), 5 (A057474), 6 (A057476), 7 (A057477), 8 (A057478), 9 (A057479), 10 (A057480), 11 (A057481), 12 (A057482), 13 (A057483).

Programs

  • Maple
    T:= proc(n) local L; L:= select(k -> Irreduc(x^n+x^k+1) mod 2, [$1..n/2]); if L = [] then -1 else op(L) fi
    end proc:
    map(T, [$2..100]); # Robert Israel, Mar 28 2017
  • Mathematica
    DeleteCases[#, 0] & /@ Table[Boole[IrreduciblePolynomialQ[x^n + x^# + 1, Modulus -> 2]] # & /@ Range[Floor[n/2]], {n, 2, 40}] /. {} -> {-1} // Flatten (* Michael De Vlieger, Mar 28 2017 *)

A278573 Irregular triangle read by rows: row n lists values of k in range 1 <= k <= n-1 such x^n + x^k + 1 is irreducible (mod 2), or -1 if no such k exists.

Original entry on oeis.org

1, 1, 2, 1, 3, 2, 3, 1, 3, 5, 1, 3, 4, 6, -1, 1, 4, 5, 8, 3, 7, 2, 9, 3, 5, 7, 9, -1, 5, 9, 1, 4, 7, 8, 11, 14, -1, 3, 5, 6, 11, 12, 14, 3, 7, 9, 11, 15, -1, 3, 5, 15, 17, 2, 7, 14, 19, 1, 21, 5, 9, 14, 18, -1, 3, 7, 18, 22, -1, -1, 1, 3, 9, 13, 15, 19, 25, 27, 2, 27, 1, 9, 21, 29, 3, 6, 7, 13
Offset: 2

Author

N. J. A. Sloane, Nov 27 2016

Keywords

Comments

Row n (if it is not -1) is invariant under the map k -> n-k. - Robert Israel, Mar 14 2018

Examples

			Triangle begins:
1,
1, 2,
1, 3,
2, 3,
1, 3, 5,
1, 3, 4, 6,
-1,
1, 4, 5, 8,
3, 7,
2, 9,
3, 5, 7, 9,
-1,
5, 9,
1, 4, 7, 8, 11, 14,
-1,
3, 5, 6, 11, 12, 14,
3, 7, 9, 11, 15,
-1,
3, 5, 15, 17,
2, 7, 14, 19,
1, 21,
...
		

References

  • Alanen, J. D., and Donald E. Knuth. "Tables of finite fields." Sankhyā: The Indian Journal of Statistics, Series A (1964): 305-328.
  • John Brillhart, On primitive trinomials (mod 2), unpublished Bell Labs Memorandum, 1968.
  • Marsh, Richard W. Table of irreducible polynomials over GF (2) through degree 19. Office of Technical Services, US Department of Commerce, 1957.

Programs

  • Maple
    for n from 2 to 30 do
      S:= select(k -> Irreduc(x^n+x^k+1) mod 2, [$1..n-1]);
      if S = [] then print(-1) else print(op(S)) fi
    od: # Robert Israel, Mar 14 2018

A136416 Numbers n such that 1+(x+1)^k+(x+1)^n is a primitive polynomial over GF(2) for some k where 0

Original entry on oeis.org

2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 15, 17, 18, 20, 21, 22, 23, 25, 28, 29, 31, 33, 35, 36, 39, 41, 42, 47, 49, 52, 54, 55, 57, 58, 60, 62, 63, 65, 66, 68, 71, 73, 74, 76, 79, 81, 84, 86, 87, 89, 92, 93, 94, 95, 97, 98, 100, 102, 103, 105, 106, 108, 110, 111, 113, 118, 119, 121
Offset: 1

Author

Joerg Arndt, Mar 31 2008, May 02 2009

Keywords

Comments

Iff the trinomial T(x)=1+x^k+x^n is irreducible (A073571) then the polynomial T(x+1)=1+(x+1)^k+(1+x)^n is irreducible.
The order of T(x+1) is in general different from the order of T(x).
So this sequence is different from A073726: for example, 1+(x+1)^7+(1+x)^10 is primitive but 1+(x+1)^3+(1+x)^10 is not (while 1+x^7+x^10 and 1+x^3+x^10 are mutual reciprocal and have the same order).

Examples

			10 is in the sequence because 1+(x+1)^7+(1+x)^10 is a primitive polynomial over GF(2).
		

A194125 n such that a length-n CLHCA of maximal period exists.

Original entry on oeis.org

2, 3, 4, 5, 6, 7, 9, 10, 11, 15, 17, 18, 20, 21, 22, 23, 25, 28, 29, 31, 33, 35, 36, 39, 41, 47, 49, 52, 55, 57, 58, 60, 63, 65, 68, 71, 73, 79, 81, 84, 87, 89, 93, 94, 95, 97, 98, 100, 103, 105, 106, 108, 111, 113, 118, 119, 121, 123, 124, 127, 129, 130, 132, 134, 135, 137, 142, 145, 148, 150, 151, 153, 159, 161, 167, 169, 170, 172, 174, 175, 177, 178, 183, 185, 191, 193, 194, 198, 199, 201
Offset: 1

Author

Joerg Arndt, Aug 15 2011

Keywords

Comments

A CLHCA is a cyclic linear hybrid cellular automaton (defined on p.883 of the Fxtbook, see link below). For fixed n its period depends only on the weight of its rule vector. The polynomial corresponding to a weight-w length-n CLHCA is x^n+(1+x)^w (or its reciprocal polynomial 1+x^w*(1+x)^(n-w)).
Sequence starts as A073726 (and appears to be a subset), first terms missing in this one are 140, 212, 236 (and no more <= 400).

Crossrefs

Cf. A073726 (n such that a primitive trinomial over GF(2) exists).

A283091 Maximal order of the trinomials of degree n over GF(2).

Original entry on oeis.org

3, 7, 15, 31, 63, 127, 217, 511, 1023, 2047, 3255, 8001, 11811, 32767, 63457, 131071, 262143, 520065, 1048575, 2097151, 4194303, 8388607, 16766977, 33554431, 67074049, 133693185, 268435455, 536870911, 1073215489, 2147483647, 4292868097, 8589934591, 17179312129
Offset: 2

Author

Keywords

Comments

a(n) is also the maximum length of binary linear recurrence relation b(x) = b(x-m) + b(x-n) mod 2 for all 0 < m < n. Knuth cites unpublished work of G. J. Mitchell & D. P. Moore showing that a(55) = 2^55 - 1 via m = 24.

References

  • D. E. Knuth, The Art of Computer Programming. Vol. 2, Seminumerical Algorithms.

Crossrefs

Cf. A073726.

Programs

  • PARI
    isperiodic(v)=for(k=1,#v-3, for(i=k+1,#v, if(v[i]!=v[i-k], next(2))); return(k))
    T(n,m,len=2^n+7)=my(v=vectorsmall(len)); v[n]=1; for(k=n+1,#v, v[k]=(v[k-n]+v[k-m])%2); v=isperiodic(v); if(v,v,T(n,m,2*len+1))
    a(n)=my(mx=T(n,1)); for(m=2,n-1,mx=max(T(n,m),mx)); mx

Formula

a(n) <= 2^n - 1, with equality if and only if n is a term of A073726.

Extensions

a(26)-a(34) from Hiroaki Yamanouchi, Apr 06 2017
Showing 1-10 of 10 results.