1,1

Equivalently, integers n such that 2^n - 1 is prime.

It is believed (but unproved) that this sequence is infinite. The data suggest that the number of terms up to exponent N is roughly K log N for some constant K.

Length of prime repunits in base 2.

The associated perfect number N=2^(p-1)*M(p) (=A019279*A000668=A000396), has 2p (=A061645) divisors with harmonic mean p (and geometric mean sqrt(N)). - Lekraj Beedassy, Aug 21 2004

In one of his first publications Euler found the numbers up to 31 but erroneously included 41 and 47.

Equals number of bits in binary expansion of n-th Mersenne prime (A117293). - Artur Jasinski, Feb 09 2007

Number of divisors of n-th even perfect number, divided by 2. Number of divisors of n-th even perfect number that are powers of 2. Number of divisors of n-th even perfect number that are multiples of n-th Mersenne prime A000668(n). - Omar E. Pol, Feb 24 2008

Number of divisors of n-th even superperfect number A061652(n). Numbers of divisors of n-th superperfect number A019279(n), assuming there are no odd superperfect numbers. - Omar E. Pol, Mar 01 2008

Differences between exponents when the even perfect numbers are represented as differences of powers of 2, for example: The 5th even perfect number is 33550336 = 2^25 - 2^12 then a(5)=25-12=13 (see A135655, A133033, A090748). - Omar E. Pol, Mar 01 2008

Number of 1's in binary expansion of n-th even perfect number (see A135650). Number of 1's in binary expansion of divisors of n-th even perfect number that are multiples of n-th Mersenne prime A000668(n) (see A135652, A135653, A135654, A135655). - Omar E. Pol, May 04 2008

Indices of the numbers A006516 that are also even perfect numbers. - Omar E. Pol, Aug 30 2008

Indices of Mersenne numbers A000225 that are also Mersenne primes A000668. - Omar E. Pol, Aug 31 2008

A modification of the Eberhart's conjecture proposed by Wagstaff (1983) which proposes that if q_n is the n-th prime such that M_(q_n) is a Mersenne prime, then q_n is approximately (2^(e^(-gamma)))^n, where gamma is the Euler-Mascheroni constant. [Weisstein, Wagstaff's Conjecture, see link below] - Jonathan Vos Post, Sep 10 2010

The (prime) number p appears in this sequence if and only if there is no prime q<2^p-1 such that the order of 2 modulo q equals p; a special case is that if p=4k+3 is prime and also q=2p+1 is prime then the order of 2 modulo q is p so p is not a term of this sequence. - Joerg Arndt, Jan 16 2011

Primes p such that sigma(2^p) - sigma(2^p-1) = 2^p-1. - Jaroslav Krizek, Aug 02 2013

T. M. Apostol, Introduction to Analytic Number Theory, Springer-Verlag, 1976, page 4.

Bateman, P. T.; Selfridge, J. L.; Wagstaff, S. S., Jr. The new Mersenne conjecture. Amer. Math. Monthly 96 (1989), no. 2, 125--128. MR0992073 (90c:11009)

J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.

Gillies, Donald B. Three new Mersenne primes and a statistical theory. Mathematics of Computation 18.85 (1964): 93-97.

F. Lemmermeyer, Reciprocity Laws From Euler to Eisenstein, Springer-Verlag, 2000, p. 57.

Mullin, Albert A. Letter to the editor: "The new Mersenne conjecture'' [Amer. Math. Monthly 96 (1989), no. 2, 125-128; MR0992073 (90c:11009)] by P. T. Bateman, J. L. Selfridge and S. S. Wagstaff, Jr., Amer. Math. Monthly 96 (1989), no. 6, 511. MR0999415 (90f:11008)

Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 19.

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).

B. Tuckerman, The 24th Mersenne prime, Notices Amer. Math. Soc., 18 (Jun, 1971), Abstract 684-A15, p. 608.

K. Zsigmondy, Zur Theorie der Potenreste, Monatsh. Math., 3 (1892), 265-284.

David Wasserman, Table of n, a(n) for n = 1..44 [Updated by N. J. A. Sloane, Feb 06 2013, Alois P. Heinz, May 01 2014, Jan 11 2015]

J. Bernheiden, Mersenne Numbers (Text in German)

Andrew R. Booker, The Nth Prime Page

J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.

P. G. Brown, A Note on Ramanujan's (FALSE) Conjectures Regarding 'Mersenne Primes'

C. K. Caldwell, Mersenne Primes

C. K. Caldwell, Recent Mersenne primes

L. Euler, Observations on a theorem of Fermat and others on looking at prime numbers

L. Euler, Observationes de theoremate quodam Fermatiano aliisque ad numeros primos spectantibus

G. Everest et al., Primes generated by recurrence sequences, arXiv:math/0412079 [math.NT], 2006.

G. Everest et al., Primes generated by recurrence sequences, Amer. Math. Monthly, 114 (No. 5, 2007), 417-431.

GIMPS (Great Internet Mersenne Prime Search), Distributed Computing Projects

GIMPS, Milestones Report

GIMPS, 48th Known Mersenne Prime Discovered, GIMPS Project Discovers Largest Known Prime Number, 2^57885161 - 1

Wilfrid Keller, List of primes k.2^n - 1 for k < 300

H. Lifchitz, Mersenne and Fermat primes field

A. J. Menezes, P. C. van Oorschot and S. A. Vanstone, Handbook of Applied Cryptography, CRC Press, 1996; see p. 143.

R. Mestrovic, Euclid's theorem on the infinitude of primes: a historical survey of its proofs (300 BC--2012) and another new proof, arXiv preprint arXiv:1202.3670, 2012 - From N. J. A. Sloane, Jun 13 2012

G. P. Michon, Perfect Numbers, Mersenne Primes

M. Oakes, A new series of Mersenne-like Gaussian primes

Omar E. Pol, Determinacion geometrica de los numeros primos y perfectos.

K. Schneider, PlanetMath.org, Mersenne numbers

H. J. Smith, Mersenne Primes

B. Tuckerman, The 24th Mersenne prime, Proc. Nat. Acad. Sci. USA, 68 (1971), 2319-2320.

H. S. Uhler, On All Of Mersenne's Numbers Particularly M_193

H. S. Uhler, First Proof That The Mersenne Number M_157 Is Composite

S. S. Wagstaff, Jr., The Cunningham Project

Eric Weisstein's World of Mathematics, Mersenne Prime

Eric Weisstein's World of Mathematics, Cunningham Number

Eric Weisstein's World of Mathematics, Integer Sequence Primes

Eric Weisstein's World of Mathematics, Repunit

Eric Weisstein's World of Mathematics, Mathworld Headline News, 40th Mersenne Prime Announced

Eric Weisstein's World of Mathematics, Mathworld Headline News, 41st Mersenne Prime Announced

Eric Weisstein, MathWorld Headline News, 42nd Mersenne Prime Found

Eric Weisstein, MathWorld Headline News, 43rd Mersenne Prime Found

Eric Weisstein, MathWorld Headline News, 44th Mersenne Prime Found

Eric Weisstein, MathWorld Headline News, 45th and 46th Mersenne Primes Found [From Lekraj Beedassy, Sep 18 2008]

Eric Weisstein, MathWorld Headline News, 47th Known Mersenne Prime Apparently Discovered [From Lekraj Beedassy, Aug 03 2009]

Eric W. Weisstein, Wagstaff's Conjecture, [From Jonathan Vos Post, Sep 10 2010]

David Whitehouse, Number takes prime position (2^13466917 - 1 found after 13000 years of computer time)

Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

a(n) = log((1/2)*(1+sqrt(1+8*A000396(n))))/log(2). - Artur Jasinski, Sep 23 2008 (under the assumption there are no odd perfect numbers, Joerg Arndt, Feb 23 2014)

a(n) = A000005(A061652(n)). - Omar E. Pol, Aug 26 2009

a(n) = A000120(A000396(n)), assuming there are no odd perfect numbers. - Omar E. Pol, Oct 30 2013

a(n) = 1 + Sum_{m=1..L(n)}(abs(n-S(m))-abs(n-S(m)-1/2)+1/2), where S(m) = Sum_{k=1..m}(A010051(k)*A010051(2^k-1)) and L(n) >= a(n)-1.  L(n) can be any function of n which satisfies the inequality. - Timothy Hopper, Jun 11 2015.

a(n) = A260073(A000396(n)) + 1, again assuming there are no odd perfect numbers. - Juri-Stepan Gerasimov, Aug 29 2015.

a(n) = A050475(n) - 1. - _Mohammed Bouayoun_, Mar 19 2004.

Corresponding to the initial terms 2, 3, 5, 7, 13, 17, 19, 31 ... we get the Mersenne primes 2^2 - 1 = 3, 2^3 - 1 = 7, 2^5 - 1 = 31, 127, 8191, 131071, 524287, 2147483647 ... (see A000668).

Select[ Prime@ Range@ 1000, PrimeQ[2^# - 1] &] (* Vladimir Joseph Stephan Orlovsky, Apr 29 2008 and modified by Robert G. Wilson v, Jan 20 2014 *)

Flatten[Position[EulerPhi[2^# - 2] + 2 == EulerPhi[2^#]&/@Range[1, 5000], True] - 1] (* Vincenzo Librandi, Aug 31 2015 *)

(PARI) isA000043(n) = isprime(2^n-1) \\ Michael B. Porter, Oct 28 2009

(PARI)

LL(e)=

{ /* Lucas-Lehmer test for exponent e */

    local(n, h);

    n = 2^e-1;

    h = Mod(2, n);

    for (k=1, e-2, h=2*h*h-1);

    return( 0==h );

}

forprime(e=2, 5000, if(LL(e), print1(e, ", "))); /* terms<5000, takes 10 secs */

/* Joerg Arndt, Jan 16 2011 */

(PARI) is(n)=my(h=Mod(2, 2^n-1)); for(i=1, n-2, h=2*h^2-1); h==0||n==2 \\ Charles R Greathouse IV, Jun 05 2013

See A000668 for the actual primes, A028335 for their lengths.

Cf. A001348, A016027, A046051, A057429, A057951-A057958, A066408, A117293, A127962, A127963, A127964, A127965, A127961, A000979, A000978, A124400, A124401, A127955, A127956, A127957, A127958, A127936, A134458, A000225, A000396, A090748, A133033, A135655, A006516, A019279, A061652, A133033, A135650, A135652, A135653, A135654, A260073, A050475.

Sequence in context: A123856 A120857 A233516 * A109799 A152961 A109461

Adjacent sequences:  A000040 A000041 A000042 * A000044 A000045 A000046

hard,nonn,nice,core,changed

N. J. A. Sloane

2^6972593 - 1 is known to be the 38th Mersenne prime. - Harry J. Smith, Apr 17 2003

2^13466917 - 1 is known to be the 39th Mersenne prime.

Also in the sequence: p=20996011, for which M(p) is a 6.3 million digit number [Nov 17 2003]. Known to be the 40th Mersenne prime since July 2010. See the GIMPS link for details.

Also in the sequence: p=24036583 (for which M(p) is a 7.2 million digit number) [Jun 01 2004]. Known (double-checked) to be the 41st Mersenne prime since Dec 01 2011. - Jason Kimberley, Jan 05 2012

Also in the sequence: p=25964951 (for which M(p) is a 7.8 million digit number). - Feb 26 2005

Also in the sequence: p=30402457 (for which M(p) is a 9.2 million digit number). - Dec 29 2005

Also in the sequence: p=32582657. - Sep 21 2006

Also in the sequence: p=37156667 and p=43112609. - Sep 15 2008

As of Dec 30 2005 the exhaustive search been run through 16693000, according to the GIMPS status page (thanks to R. K. Guy for this information). - N. J. A. Sloane, Dec 30 2005

Also in the sequence: p=42643801 (April 2009).

Also in the sequence: p=57885161 (Jan 25 2013).

Added 30402457, now known to be a(43), Joerg Arndt, Mar 04 2014

Added a(44), verified by GIMPS [via Tony Noe], by Charles R Greathouse IV, Nov 10 2014

approved