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.

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A001917 (p-1)/x, where p = prime(n) and x = ord(2,p), the smallest positive integer such that 2^x == 1 (mod p).

Original entry on oeis.org

1, 1, 2, 1, 1, 2, 1, 2, 1, 6, 1, 2, 3, 2, 1, 1, 1, 1, 2, 8, 2, 1, 8, 2, 1, 2, 1, 3, 4, 18, 1, 2, 1, 1, 10, 3, 1, 2, 1, 1, 1, 2, 2, 1, 2, 1, 6, 1, 3, 8, 2, 10, 5, 16, 2, 1, 2, 3, 4, 3, 1, 3, 2, 2, 1, 11, 16, 1, 1, 4, 2, 2, 1, 1, 2, 1, 9, 2, 2, 1, 1, 10, 6, 6, 1, 2, 6, 1, 2, 1, 2, 2, 1, 3, 2, 1, 2, 1, 1, 1, 1, 1, 2
Offset: 2

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Author

Keywords

Comments

Also number of cycles in permutations constructed from siteswap juggling pattern 1234...p.
Also the number of irreducible polynomial factors for the polynomial (x^p-1)/(x-1) over GF(2), where p is the n-th prime. - V. Raman, Oct 04 2012
The sequence is unbounded: for any value of M, there exists an element of the sequence divisible by M. See the proof by David Speyer below. - Shreevatsa R, May 24 2013

References

  • M. Kraitchik, Recherches sur la Théorie des Nombres. Gauthiers-Villars, Paris, Vol. 1, 1924, Vol. 2, 1929, see Vol. 1, p. 131.
  • D. H. Lehmer, Guide to Tables in the Theory of Numbers. Bulletin No. 105, National Research Council, Washington, DC, 1941, pp. 7-10.
  • W. Meissner, Über die Teilbarkeit von 2^p-2 durch das Quadrat der Primzahl p = 1093, Sitzungsberichte Königlich Preussischen Akadamie Wissenschaften Berlin, 35 (1913), 663-667.
  • 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

Cf. A006694 gives cycle counts of such permutations constructed for all odd numbers.
Cf. A014664.

Programs

  • Magma
    [ (p-1)/Modorder(2, p) where p is NthPrime(n): n in [2..100] ]; // Klaus Brockhaus, Dec 09 2008
    
  • Maple
    with(numtheory); [seq((ithprime(n)-1)/order(2,ithprime(n)),n=2..130)];
    with(group); with(numtheory); gen_rss_perm := proc(n) local a, i; a := []; for i from 1 to n do a := [op(a), ((2*i) mod (n+1))]; od; RETURN(a); end; count_of_disjcyc_seq := [seq(nops(convert(gen_rss_perm(ithprime(j)-1),'disjcyc')),j=2..)];
  • Mathematica
    a6694[n_] := Sum[ EulerPhi[d] / MultiplicativeOrder[2, d], {d, Divisors[2n + 1]}] - 1; a[n_] := a6694[(Prime[n]-1)/2]; Table[ a[n], {n, 2, 104}] (* Jean-François Alcover, Dec 14 2011, after Vladimir Shevelev *)
    Table[p = Prime[n]; (p - 1)/MultiplicativeOrder[2, p], {n, 2, 100}] (* T. D. Noe, Apr 11 2012 *)
    ord[n_]:=Module[{x=1},While[PowerMod[2,x,n]!=1,x++];(n-1)/x]; ord/@ Prime[ Range[ 2,110]] (* Harvey P. Dale, Jun 25 2014 *)
  • PARI
    {for(n=2, 100, p=prime(n); print1((p-1)/znorder(Mod(2, p)), ","))} \\ Klaus Brockhaus, Dec 09 2008
    
  • Python
    from sympy import prime, n_order
    def A001917(n):
        p = prime(n)
        return 1 if n == 2 else (p-1)//n_order(2,p) # Chai Wah Wu, Jan 15 2020

Formula

From Vladimir Shevelev, May 26 2008: (Start)
a(n) = A006694((p_n-1)/2) where p_n is the n-th odd prime.
Conjecture: k*a(n) = A006694(((p_n)^k-1)/2). (End)

Extensions

Additional comments from Antti Karttunen, Jan 05 2000
More terms from N. J. A. Sloane, Dec 24 2009

A061741 Primes with 39 as smallest positive primitive root.

Original entry on oeis.org

166031, 264961, 325249, 388081, 450071, 462841, 543601, 735271, 816649, 823201, 915049, 1063561, 1155151, 1414081, 1415929, 1554169, 1704271, 1884121, 1952449, 2181271, 2215921, 2290831, 2477521, 2499421, 2514961, 2585647, 2633689
Offset: 1

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Author

Klaus Brockhaus, May 06 2001

Keywords

Crossrefs

Programs

  • Mathematica
    Select[ Prime@Range@221000, PrimitiveRoot@# == 39 &] (* Robert G. Wilson v, May 11 2001 *)
  • PARI
    is(n)=if(n<9||!isprime(n), return(0)); for(k=2,38,if(znorder(Mod(k,n))==n-1, return(0))); znorder(Mod(39,n))==n-1 \\ Charles R Greathouse IV, Apr 28 2015

Extensions

More terms from Robert G. Wilson v, May 11 2001 and Dec 21 2005

A114657 Primes with 40 as smallest positive primitive root.

Original entry on oeis.org

1373989, 3296581, 3771211, 4014739, 4073371, 5191033, 15188731, 19461661, 23108101, 27478621, 27945061, 39242701, 40393051, 48942661, 51113941, 60043411, 62362411, 66868621, 71443531, 73572181, 94008091, 103767691, 106066171, 110543581, 110950171, 114407101
Offset: 1

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Author

Robert G. Wilson v, Dec 21 2005

Keywords

Crossrefs

Programs

  • Mathematica
    Select[ Prime@Range@6354000, PrimitiveRoot@# == 40 &]

Extensions

a(23)-a(26) from Robert Price, Nov 18 2023

A114686 Primes with 71 as smallest positive primitive root.

Original entry on oeis.org

3659401, 8453041, 10319761, 14155681, 16391761, 18094561, 19616689, 20456329, 21677041, 22628929, 27275161, 32051881, 34228489, 37728601, 38884561, 39191881, 40101071, 40167241, 42163969, 47931601, 48461449, 49460161, 50389441, 54932329, 56219281, 57590569
Offset: 1

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Author

Robert G. Wilson v, Dec 21 2005

Keywords

Crossrefs

Programs

  • Mathematica
    t={}; Do[ If[ PrimitiveRoot[ Prime@n] == 71, AppendTo[t, n]; Print@ Prime@n], {n, 3280000}]; Prime@t
  • PARI
    is(n)=if(n<72,return(0));for(k=2,70,if(znorder(Mod(k,n))==n-1,return(0)));znorder(Mod(71,n))==n-1&&isprime(n) \\ Charles R Greathouse IV, Jul 19 2011
    
  • PARI
    is(n)=isprime(n)&&lift(znprimroot(n))==71 \\ relies on implementation details, may not always work
    \\ Charles R Greathouse IV, Jul 19 2011

Extensions

a(23) and beyond from Robert Price, Nov 20 2023

A167791 Numbers with primitive root 2.

Original entry on oeis.org

3, 5, 9, 11, 13, 19, 25, 27, 29, 37, 53, 59, 61, 67, 81, 83, 101, 107, 121, 125, 131, 139, 149, 163, 169, 173, 179, 181, 197, 211, 227, 243, 269, 293, 317, 347, 349, 361, 373, 379, 389, 419, 421, 443, 461, 467, 491, 509, 523, 541, 547, 557, 563, 587, 613, 619
Offset: 1

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Author

T. D. Noe, Nov 12 2009

Keywords

Comments

Numbers k such that the binary expansion of 1/k has period phi(k). For example 1/27 has a period of 18 bits.
All entries are odd. An odd composite number n can have a primitive root if and only if it is a prime power (see A033948). - V. Raman, Oct 04 2012
It is unknown whether there is a prime p such that p is in this sequence while p^2 is not. - Jianing Song, Jan 27 2019

Crossrefs

Cf. A000010, A001122 (primes with primitive root 2), A033948.

Programs

  • Magma
    [n: n in [3..619] | IsPrimitive(2, n)]; // Arkadiusz Wesolowski, Dec 22 2020
  • Mathematica
    pr=2; Select[Range[2,2000], MultiplicativeOrder[pr,# ] == EulerPhi[ # ] &]
  • PARI
    for(n=3,200,if(n%2==1&&znorder(Mod(2,n))==eulerphi(n),printf(n","))) \\ V. Raman, Oct 04 2012
    
  • PARI
    is(n)=n%2 && isprimepower(n) && znorder(Mod(2,n))==eulerphi(n-1) \\ Charles R Greathouse IV, Jul 05 2013
    

A019334 Primes with primitive root 3.

Original entry on oeis.org

2, 5, 7, 17, 19, 29, 31, 43, 53, 79, 89, 101, 113, 127, 137, 139, 149, 163, 173, 197, 199, 211, 223, 233, 257, 269, 281, 283, 293, 317, 331, 353, 379, 389, 401, 449, 461, 463, 487, 509, 521, 557, 569, 571, 593, 607, 617, 631, 641, 653, 677, 691, 701, 739, 751, 773, 797
Offset: 1

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Comments

To allow primes less than the specified primitive root m (here, 3) to be included, we use the essentially equivalent definition "Primes p such that the multiplicative order of m mod p is p-1". This comment applies to all of A019334-A019421. - N. J. A. Sloane, Dec 02 2019
From Jianing Song, Apr 27 2019: (Start)
All terms except the first are congruent to 5 or 7 modulo 12. If we define
Pi(N,b) = # {p prime, p <= N, p == b (mod 12)};
Q(N) = # {p prime, 2 < p <= N, p in this sequence},
then by Artin's conjecture, Q(N) ~ C*N/log(N) ~ 2*C*(Pi(N,5) + Pi(N,7)), where C = A005596 is Artin's constant.
If we further define
Q(N,b) = # {p prime, p <= N, p == b (mod 12), p in this sequence},
then we have:
Q(N,5) ~ (3/5)*Q(N) ~ (12/5)*C*Pi(N,5);
Q(N,7) ~ (2/5)*Q(N) ~ ( 8/5)*C*Pi(N,7).
For example, for the first 1000 terms except for a(1) = 2, there are 593 terms == 5 (mod 12) and 406 terms == 7 (mod 12). (End)

Crossrefs

Cf. A005596, A001122 (primitive root 2).

Programs

  • Mathematica
    pr=3; Select[Prime[Range[200]], MultiplicativeOrder[pr, # ] == #-1 &]
  • PARI
    isok(p) = isprime(p) && (p!=3) && (znorder(Mod(3, p))+1 == p); \\ Michel Marcus, May 12 2019

A006883 Long period primes: the decimal expansion of 1/p has period p-1.

Original entry on oeis.org

2, 7, 17, 19, 23, 29, 47, 59, 61, 97, 109, 113, 131, 149, 167, 179, 181, 193, 223, 229, 233, 257, 263, 269, 313, 337, 367, 379, 383, 389, 419, 433, 461, 487, 491, 499, 503, 509, 541, 571, 577, 593, 619, 647, 659, 701, 709, 727, 743, 811, 821, 823, 857, 863
Offset: 1

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Keywords

Comments

Also called full reptend primes or maximal period primes.
Also called golden primes or long primes.
Here, as opposed to A001913, 2 is a term, because the decimal expansion of 1/2 is 0.5000000000..., so it is periodic with period 1 and pattern 0. - Michel Marcus, Jun 06 2018

References

  • M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 864.
  • Albert H. Beiler, Recreations in the Theory of Numbers, 2nd ed. New York: Dover, 1966, pages 65, 309.
  • John H. Conway and R. K. Guy, The Book of Numbers, Copernicus Press, p. 161.
  • Carl Friedrich Gauss, "Disquisitiones Arithmeticae"
  • G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, p. 115.
  • M. Kraitchik, Recherches sur la Théorie des Nombres. Gauthiers-Villars, Paris, Vol. 1, 1924, Vol. 2, 1929, see Vol. 1, p. 61.
  • D. H. Lehmer, A note on primitive roots, Scripta Mathematica, vol. 26 (1963), p. 117. [Gives some interesting information about the frequency of maximal period primes and discusses two freak cases.]
  • C. Stanley Ogilvy and John T. Anderson, Excursions in Number Theory, Oxford University Press, 1966, pp. 56-58.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Apart from initial term, identical to A001913.
Cf. A001122 (long period primes in binary).

Programs

  • Maple
    isA006883 := proc(p) if p = 2 then true; elif isprime(p) then RETURN( numtheory[order](10,p) = p-1) ; else false; fi; end: for i from 1 to 300 do p := ithprime(i) ; if isA006883(p) then printf("%d ",p) ; fi; od: # R. J. Mathar, Apr 01 2009
  • Mathematica
    f[n_Integer] := Block[{ds = Divisors[n - 1]}, (n - 1)/Take[ ds, Position[ PowerMod[ 10, ds, n], 1] [[1, 1]]] [[ -1]]]; Select[ Prime[ Range[4, 150]], f[ # ] == 1 &] (* Robert G. Wilson v, Sep 14 2004 *)
    maxPeriodQ[p_] := MultiplicativeOrder[10, p] == p-1; maxPeriodQ[2] = True; Select[ Prime[ Range[150]], maxPeriodQ] (* Jean-François Alcover, Jan 07 2013 *)
  • PARI
    print1(2);forprime(p=7,1e3,if(znorder(Mod(10,p))+1==p,print1(", "p))) \\ Charles R Greathouse IV, Feb 27 2011

Formula

From Gerard Schildberger, Jul 02 2005: (Start)
Emil Artin conjectured that the proportion of primes that belong to this sequence can be expressed as:
(2*1-1)(3*2-1)(5*4-1)(7*6-1)(11*10-1)(13*12-1)...
------------------------------------------------- = 0.373955813619202288...
(2*1)(3*2)(5*4)(7*6)(11*10)(13*12)...
(End)
This Artin's constant, Product_{p prime} (1-1/(p^2-p)), is referenced in A005596. - Robert FERREOL, Jun 05 2018

Extensions

More terms from James Sellers, Aug 21 2000
Additional comments from Jason Earls, Apr 06 2001

A112927 a(n) is the least prime such that the multiplicative order of 2 mod a(n) equals n, or a(n)=1 if no such prime exists.

Original entry on oeis.org

1, 3, 7, 5, 31, 1, 127, 17, 73, 11, 23, 13, 8191, 43, 151, 257, 131071, 19, 524287, 41, 337, 683, 47, 241, 601, 2731, 262657, 29, 233, 331, 2147483647, 65537, 599479, 43691, 71, 37, 223, 174763, 79, 61681, 13367, 5419, 431, 397, 631, 2796203, 2351, 97, 4432676798593, 251, 103, 53, 6361, 87211
Offset: 1

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Author

Vladimir Shevelev, Aug 25 2008

Keywords

Comments

If a(n) differs from 1, then a(n) is the minimal prime divisor of A064078(n);
a(n)=n+1 iff n+1 is prime from A001122; a(n)=2n+1 iff 2n+1 is prime from A115591.
If a(n) > 1 then a(n) is the index where n occurs first in A014664. - M. F. Hasler, Feb 21 2016
Bang's theorem (special case of Zsigmondy's theorem, see links): a(n)>1 for all n>6. - Jeppe Stig Nielsen, Aug 31 2020

Crossrefs

Cf. A112927 (base 2), A143663 (base 3), A112092 (base 4), A143665 (base 5), A379639 (base 6), A379640 (base 7), A379641 (base 8), A379642 (base 9), A007138 (base 10), A379644 (base 11), A252170 (base 12).

Programs

  • PARI
    A112927(n,f=factor(2^n-1)[,1])=!for(i=1,#f,znorder(Mod(2,f[i]))==n&&return(f[i])) \\ Use the optional 2nd arg to give a list of pseudoprimes to try when factoring of 2^n-1 is too slow. You may try factor(2^n-1,0)[,1]. - M. F. Hasler, Feb 21 2016

A023212 Primes p such that 4*p+1 is also prime.

Original entry on oeis.org

3, 7, 13, 37, 43, 67, 73, 79, 97, 127, 139, 163, 193, 199, 277, 307, 373, 409, 433, 487, 499, 577, 619, 673, 709, 727, 739, 853, 883, 919, 997, 1033, 1039, 1063, 1087, 1093, 1123, 1129, 1297, 1327, 1423, 1429, 1453, 1543, 1549, 1567, 1579, 1597, 1663, 1753
Offset: 1

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Keywords

Comments

If p > 3 is a Sophie Germain prime (A005384), p cannot be in this sequence, because all Germain primes greater than 3 are of the form 6k - 1, and then 4p + 1 = 3*(8k-1). - Enrique Pérez Herrero, Aug 15 2011
a(n), except 3, is of the form 6k+1. - Enrique Pérez Herrero, Aug 16 2011
According to Beiler: the integer 2 is a primitive root of all primes of the form 4p + 1 with p prime. - Martin Renner, Nov 06 2011
Chebyshev showed that 2 is a primitive root of all primes of the form 4p + 1 with p prime. - Jonathan Sondow, Feb 04 2013
Also solutions to the equation: floor(4/A000005(4*n^2+n)) = 1. - Enrique Pérez Herrero, Jan 12 2013
Prime numbers p such that p^p - 1 is divisible by 4*p + 1. - Gary Detlefs, May 22 2013
It appears that whenever (p^p - 1)/(4*p + 1) is an integer, then this integer is even (see previous comment). - Alexander R. Povolotsky, May 23 2013
4p + 1 does not divide p^n + 1 for any n. - Robin Garcia, Jun 20 2013
Primes in this sequence of the form 4k+1 are listed in A113601. - Gary Detlefs, May 07 2019
There are no numbers with last digit 1 in this list (i.e., members of A030430) because primes p == 1 (mod 10) lead to 5|(4p+1) such that 4p+1 is not prime. - R. J. Mathar, Aug 13 2019

References

  • Albert H. Beiler, Recreations in the theory of numbers, New York: Dover, (2nd ed.) 1966, p. 102, nr. 5.
  • P. L. Chebyshev, Theory of congruences, Elements of number theory, Chelsea, 1972, p. 306.

Crossrefs

Programs

  • Magma
    [n: n in [0..1000] | IsPrime(n) and IsPrime(4*n+1)]; // Vincenzo Librandi, Nov 20 2010
    
  • Maple
    isA023212 := proc(n)
        isprime(n) and isprime(4*n+1) ;
    end proc:
    for n from 1 to 1800 do
        if isA023212(n) then
            printf("%d,",n) ;
        end if;
    end do: # R. J. Mathar, May 26 2013
  • Mathematica
    Select[Range[2000], PrimeQ[#] && PrimeQ[4# + 1] &] (* Alonso del Arte, Aug 15 2011 *)
    Join[{3}, Select[Range[7, 2000, 6], PrimeQ[#] && PrimeQ[4# + 1] &]] (* Zak Seidov, Jan 21 2012 *)
    Select[Prime[Range[300]],PrimeQ[4#+1]&] (* Harvey P. Dale, Oct 17 2021 *)
  • PARI
    forprime(p=2,1800,if(Mod(p,4*p+1)^p==1, print1(p", \n"))) \\ Alexander R. Povolotsky, May 23 2013

Formula

Sum_{n>=1} 1/a(n) is in the interval (0.892962433, 1.1616905) (Wagstaff, 2021). - Amiram Eldar, Nov 04 2021

Extensions

Name edited by Michel Marcus, Nov 27 2020

A115591 Primes p such that the multiplicative order of 2 modulo p is (p-1)/2.

Original entry on oeis.org

7, 17, 23, 41, 47, 71, 79, 97, 103, 137, 167, 191, 193, 199, 239, 263, 271, 311, 313, 359, 367, 383, 401, 409, 449, 463, 479, 487, 503, 521, 569, 599, 607, 647, 719, 743, 751, 761, 769, 809, 823, 839, 857, 863, 887, 929, 967, 977, 983, 991, 1009, 1031
Offset: 1

Views

Author

Don Reble, Mar 11 2006

Keywords

Comments

It appears that this is also the sequence of values of n for which the sum of terms of one period of the base-2 MR-expansion (see A136042) of 1/n equals (n-1)/2. An example appears in A155072 where one period of the base-2 MR-expansion of 1/17 is shown to be {5,1,1,1} with sum 8=(17-1)/2. - John W. Layman, Jan 19 2009
If p is a term of this sequence, then 2 is a quadratic residue module p, so p == 1, 7 (mod 8). - Jianing Song, Nov 01 2024

Crossrefs

Cf. A136042, A155072. - John W. Layman, Jan 19 2009

Programs

  • Magma
    [ p: p in PrimesUpTo(1031) | r eq 1 and Order(R!2) eq q where q,r is Quotrem(p,2) where R is ResidueClassRing(p) ]; // Klaus Brockhaus, Dec 02 2008
    
  • Mathematica
    fQ[n_] := 1 + 2 MultiplicativeOrder[2, n] == n; Select[ Prime@ Range@ 174, fQ]
  • PARI
    r=2;forprime(p=3,1500,z=(p-1)/znorder(Mod(r,p));if(z==2,print1(p,", "))); \\ Joerg Arndt, Jan 12 2011
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