

A000040


The prime numbers.
(Formerly M0652 N0241)


7898



2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271
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OFFSET

1,1


COMMENTS

See A065091 for comments, formulas etc. concerning only odd primes. For all information concerning prime powers, see A000961. For contributions concerning "almost primes" see A002808.
A number n is prime if it is greater than 1 and has no positive divisors except 1 and n.
A natural number is prime if and only if it has exactly two (positive) divisors.
A prime has exactly one proper positive divisor, 1.
The sum of an odd number > 1 (2i+1, i >= 1) of consecutive positive odd numbers centered on the jth odd number >= 2i+1 (2j+1, j >= i) being (2i+1)*(2j+1) has 2 or more odd prime factors (odd semiprime iff 2i+1 and 2j+1 are primes).  Daniel Forgues, Jul 15 2009
The paper by Kaoru Motose starts as follows: "Let q be a prime divisor of a Mersenne number 2^p1 where p is prime. Then p is the order of 2 (mod q). Thus p is a divisor of q  1 and q > p. This shows that there exist infinitely many prime numbers."  Pieter Moree, Oct 14 2004
1 is not a prime, for if the primes included 1, then the factorization of a natural number n into a product of primes would not be unique, since n = n*1.
1 is the empty product (has 0 prime factors), whereas a prime has 1 prime factor (itself).  Daniel Forgues, Jul 23 2009
Prime(n) and pi(n) are inverse functions: A000720(a(n)) = n and a(n) is the least number m such that a(A000720(m)) = a(n). a(A000720(n)) = n if (and only if) n is prime.
Elementary primality test: If no prime <= sqrt(m) divides m, then m is prime (since a prime is its own exclusive multiple, apart from 1).  Lekraj Beedassy, Mar 31 2005
Second sequence ever computed by electronic computer, on EDSAC, May 09 1949 (see Renwick link).  Russ Cox, Apr 20 2006
Every prime p > 3 is a linear combination of previous primes prime(n) with nonzero coefficients c(n) and c(n) < prime(n).  Amarnath Murthy, Franklin T. AdamsWatters and Joshua Zucker, May 17 2006; clarified by Chayim Lowen, Jul 17 2015
There is a unique decomposition of the primes: provided the weight A117078(n) is > 0, we have prime(n) = weight * level + gap, or A000040(n) = A117078(n) * A117563(n) + A001223(n).  Rémi Eismann, Feb 16 2007
Equals row sums of triangle A143350.  Gary W. Adamson, Aug 10 2008
APSO (Alternating partial sums of sequence) ab+cd+ef+g... = (a+b+c+d+e+f+g...)2*(b+d+f...): APSO(A000040) = A008347=A007504  2*(A077126 repeated) (A007504A008347)/2 = A077131 alternated with A077126.  Eric Desbiaux, Oct 28 2008
The Greek transliteration of 'Prime Number' is 'Proton Arithmon'.  Daniel Forgues, May 08 2009
It appears that, with the BachetBezout theorem, A000040 = (2*A039701) + (3*A157966).  Eric Desbiaux, Nov 15 2009
a(n) = A008864(n)  1 = A052147(n)  2 = A113395(n)  3 = A175221(n)  4 = A175222(n)  5 = A139049(n)  6 = A175223(n)  7 = A175224(n)  8 = A140353(n)  9 = A175225(n)  10.  Jaroslav Krizek, Mar 06 2010
2 and 3 might be referred to as the two "forcibly prime numbers" since there are no integers greater than 1 and less than or equal to their respective square roots. Not a single trial division ever needs to be done for 2 or 3, so they are disqualified from the outset from any attempt to belong to the set of composite numbers. 2 and 3 are thus the only consecutive primes. Since any further prime needs to be coprime to both 2 and 3, they must be congruent to 5 or 1 (mod 2*3) and thus must all be of the form (2*3)*k /+ 1 with k >= 1. When both (2*3)*k  1 and (2*3)*k + 1 are prime for a given k >= 1, they are referred to as twin primes (3 and 5 being the only twin primes of the form (2*2)*k  1 and (2*2)*k + 1).  Daniel Forgues, Mar 19 2010
For prime n, the sum of divisors of n > the product of divisors of n. Sigma(n)==1 (mod n).  JuriStepan Gerasimov, Mar 12 2011
Conjecture: a(n) = (6*f(n) + (1)^f(n)3)/2, n > 2, where f(n) = floor(ithprime(n)/3) + 1. See A181709.  Gary Detlefs, Dec 12 2011
A number n is prime if and only if it is different from zero and different from a unit and each multiple of n decomposes into factors such that n divides at least one of the factors. This definition has the advantage that it does not make an assertion on the number of divisors of n. It applies equally for the integers (where a prime has exactly four divisors) and the natural numbers (where a prime has exactly two divisors).  Peter Luschny, Oct 09 2012
Motivated by his conjecture on representations of integers by alternating sums of consecutive primes, for any positive integer n, ZhiWei Sun conjectured that the polynomial P_n(x)= sum_{k=0}^n a(k+1)*x^k is irreducible over the field of rational numbers with the Galois group S_n, and moreover P_n(x) is irreducible mod a(m) for some m<=n(n+1)/2. It seems that no known criterion on irreduciblity of polynomials implies this conjecture.  ZhiWei Sun, Mar 23 2013
Reading the primes (excluding 2,3,5) mod 90 divides them into 24 classes, which are described by A181732, A195993, A198382, A196000, A201804, A196007, A201734, A201739, A201819, A201816, A201817, A201818, A202104, A201820, A201822, A201101, A202113, A202105, A202110, A202112, A202129, A202114, A202115 and A202116.  J. W. Helkenberg, Jul 24 2013
The old definition of prime numbers was "positive integers that have no divisors other than 1 and itself", which gives A008578, not this sequence.  Omar E. Pol, Oct 05 2013
Questions on a(2n) and Ramanujan primes are in A233739.  Jonathan Sondow, Dec 16 2013
From Hieronymus Fischer, Apr 02 2014: (Start)
Natural numbers such that there is exactly one base b such that the baseb alternate digital sum is 0 (see A239707).
Equivalently: Numbers p > 1 such that b = p1 is the only base >= 1 for which the baseb alternate digital sum is 0.
Equivalently: Numbers p > 1 such that the baseb alternate digital sum is <> 0 for all bases 1 <= b < p1. (End)
An integer n > 1 is a prime if and only if it is not the sum of positive integers in arithmetic progression with common difference 2.  JeanChristophe Hervé, Jun 01 2014
Conjecture: Numbers having prime factors <= p(n+1) are {kk^f(n) mod primorial(n)=1}, where f(n)= LCM(p(i)1,i=1..n) = A058254(n) and primorial(n) = A002110. For example, numbers with no prime divisor <= p(7)= 17 or, equivalently, the primes < 17^2 are {kk^60/ mod 30030=1}.  Gary Detlefs, Jun 07 2014
Cramer conjecture prime(n+1)  prime(n) < C log^2 prime(n) is equivalent to the inequality (log prime(n+1)/log prime(n))^n < e^C, as n tend to infinity, where C is an absolute constant.  Thomas Ordowski, Oct 06 2014
The primes appear as the denominators of the only fractions in the table of integers and reduced fractions for: (k!/e) * Sum_{n>=0} Sum_{j=0..n} j^k/n!, k>=0, occurring at k=p1, where p is a prime, with p=2 occurring at both k=1 and k=3.  Richard R. Forberg, Dec 23 2014.
The preceding comment also applies to the zsequence of the Sheffer matrix, when multiplied by the factorial of its index. See A130190.  Richard R. Forberg, Dec 28 2014
It is easily proved that (a(n+m)^j + a(n)^k)/2 and (a(n+m)^j  a(n)^k)/2 are coprime for all m, j, k > 0 and n>1. Conjecture: All coprime pairs can be so constructed, assuming repeated division by 2 of the even number in the resulting pair until it is odd.  Richard R. Forberg, Jun 07 2015
I conjecture that for any positive rational number r there are finitely many primes q_1,...,q_k such that r = sum_{j=1..k} 1/(q_j1). For example, 2 = 1/(21)+1/(31)+1/(51)+1/(71)+1/(131) with 2, 3, 5, 7 and 13 all prime, 1/7 = 1/(131)+1/(291)+1/(431) with 13, 29 and 43 all prime, and 5/7 = 1/(31)+1/(71)+1/(311)+1/(711) with 3, 7, 31 and 71 all prime.  ZhiWei Sun, Sep 09 2015
I also conjecture that for any positive rational number r there are finitely many primes p_1,...,p_k such that r = sum_{j=1..k} 1/(p_j+1). For example, 1 = 1/(2+1)+1/(3+1)+1/(5+1)+1/(7+1)+1/(11+1)+1/(23+1) with 2, 3, 5, 7, 11 and 23 all prime, and 10/11 = 1/(2+1)+1/(3+1)+1/(5+1)+1/(7+1)+1/(43+1)+1/(131+1)+1/(263+1) with 2, 3, 5, 7, 43, 131 and 263 all prime.  ZhiWei Sun, Sep 13 2015
Prime numbers are zeros of the functions V_s(x) = Sum_{n>=1} (moebius(n) / n^s) * x^(s*omega(n)), for each s > 1.  Dimitris Valianatos, Jun 29 2016
Satisfies a(n) = 2*n + Sum_{k=1..(a(n)1)} cot(k*Pi/a(n))*sin(2*k*n^a(n)*Pi/a(n)).  Ilya Gutkovskiy, Jun 29 2016
Numbers n such that ((n2)!!)^2 == +1 (mod n).  Thomas Ordowski, Aug 27 2016
Union of A030430, A030431, A030432, A030433, {2,5}.  Muniru A Asiru, Oct 20 2016


REFERENCES

M. Aigner and G. M. Ziegler, Proofs from The Book, SpringerVerlag, Berlin, 2nd. ed., 2001; see p. 3.
T. M. Apostol, Introduction to Analytic Number Theory, SpringerVerlag, 1976, page 2.
E. Bach and Jeffrey Shallit, Algorithmic Number Theory, I, Chaps. 8, 9.
D. M. Bressoud, Factorization and Primality Testing, SpringerVerlag NY 1989.
M. Cipolla, "La determinazione asintotica dell'nmo numero primo.", Rend. d. R. Acc. di sc. fis. e mat. di Napoli, s. 3, VIII (1902), pp. 132166.
R. Crandall and C. Pomerance, Prime Numbers: A Computational Perspective, Springer, NY, 2001; see p. 1.
Martin Davis, "Algorithms, Equations, and Logic", pp. 415 of S. Barry Cooper and Andrew Hodges, Eds., "The Once and Future Turing: Computing the World", Cambridge 2016.
J.P. Delahaye, Merveilleux nombres premiers, Pour la ScienceBelin Paris, 2000.
J.P. Delahaye, Savoir si un nombre est premier: facile, Pour La Science, 303(1) 2003, pp. 98102.
M. Dietzfelbinger, Primality Testing in Polynomial Time, Springer NY 2004.
M. du Sautoy, The Music of the Primes, Fourth Estate / HarperCollins, 2003; see p. 5.
J. Elie, "L'algorithme AKS", in 'Quadrature', No. 60, pp. 2232, 2006 EDPsciences, Les Ulis (France);
Seymour. B. Elk, "Prime Number Assignment to a Hexagonal Tessellation of a Plane That Generates Canonical Names for PeriCondensed Polybenzenes", J. Chem. Inf. Comput. Sci., vol. 34 (1994), pp. 942946.
W. & F. Ellison, Prime Numbers, Hermann Paris 1985
T. Estermann, Introduction to Modern Prime Number Theory, Camb. Univ. Press, 1969.
G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, p. 2.
Peter Hilton and Jean Pedersen, A Mathematical Tapestry: Demonstrating the Beautiful Unity of Mathematics, Cambridge University Press, 2010, pp. (260264).
H. D. Huskey, Derrick Henry Lehmer [19051991]. IEEE Ann. Hist. Comput. 17 (1995), no. 2, 6468. Math. Rev. 96b:01035, cf. http://www.ams.org/mathscinetgetitem?mr=1336709
M. N. Huxley, The Distribution of Prime Numbers, Oxford Univ. Press, 1972.
D. S. Jandu, Prime Numbers And Factorization, Infinite Bandwidth Publishing, N. Hollywood CA 2007.
E. Landau, Handbuch der Lehre von der Verteilung der Primzahlen, Chelsea, NY, 1974.
D. H. Lehmer, The sieve problem for allpurpose computers. Math. Tables and Other Aids to Computation, Math. Tables and Other Aids to Computation, 7, (1953). 614. Math. Rev. 14:691e
D. N. Lehmer, "List of Prime Numbers from 1 to 10,006,721", Carnegie Institute, Washington, D.C. 1909.
W. J. LeVeque, Topics in Number Theory. AddisonWesley, Reading, MA, 2 vols., 1956, Vol. 1, Chap. 6.
H. Lifchitz, Table des nombres premiers de 0 à 20 millions (Tomes I & II), Albert Blanchard, Paris 1971.
R. F. Lukes, C. D. Patterson and H. C. Williams, Numerical sieving devices: their history and some applications. Nieuw Arch. Wisk. (4) 13 (1995), no. 1, 113139. Math. Rev. 96m:11082, cf http://www.ams.org/mathscinetgetitem?mr=96m:11082
Kaoru Motose, On values of cyclotomic polynomials. II, Math. J. Okayama Univ. 37 (1995), 2736.
P. Ribenboim, The New Book of Prime Number Records, SpringerVerlag NY 1995.
P. Ribenboim, The Little Book of Bigger Primes, SpringerVerlag NY 2004.
H. Riesel, Prime Numbers and Computer Methods for Factorization, Birkhaeuser Boston, Cambridge MA 1994.
B. Rittaud, "31415879. Ce nombre estil premier?" ['Is this number prime?'], La Recherche, Vol. 361, pp. 7073, Feb 15 2003, Paris.
D. Shanks, Solved and Unsolved Problems in Number Theory, 2nd. ed., Chelsea, 1978, Chap. 1.
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).
D. Wells, Prime Numbers: The Most Mysterious Figures In Math, J.Wiley NY 2005.
H. C. Williams and Jeffrey Shallit, Factoring integers before computers. Mathematics of Computation 19431993: a halfcentury of computational mathematics (Vancouver, BC, 1993), 481531, Proc. Sympos. Appl. Math., 48, AMS, Providence, RI, 1994. Math. Rev. 95m:11143


LINKS

N. J. A. Sloane, Table of n, prime(n) for n = 1..10000
N. J. A. Sloane, Table of n, prime(n) for n = 1..100000
M. Agrawal, N. Kayal & N. Saxena, PRIMES is in P, Annals of Maths., 160:2 (2004), pp. 781793. [alternate link]
M. Agrawal, A Short History of "PRIMES is in P"
P. Alfeld, Notes and Literature on Prime Numbers
J. W. Andrushkiw, R. I. Andrushkiw and C. E. Corzatt, Representations of Positive Integers as Sums of Arithmetic Progressions, Mathematics Magazine, Vol. 49, No. 5 (Nov., 1976), pp. 245248.
Anonymous, Prime Number Master Index (for primes up to 2*10^7)
Anonymous, prime number
P. T. Bateman & H. G. Diamond, A Hundred Years of Prime Numbers, Amer. Math. Month., Vol. 103 (9), Nov. 1996, pp. 729741.
E. R. Berlekamp, A contribution to mathematical psychometrics, Unpublished Bell Labs Memorandum, Feb 08 1968 [Annotated scanned copy]
D. J. Bernstein, Proving Primality After AgrawalKayalSaxena
D. J. Bernstein, Distinguishing prime numbers from composite numbers
P. Berrizbeitia, Sharpening "Primes is in P" for a large family of numbers, arXiv:math/0211334 [math.NT], 2002.
A. Booker, The Nth Prime Page
F. Bornemann, PRIMES Is in P: A Breakthrough for "Everyman"
A. Bowyer, Formulae for Primes [broken link ?]
B. M. Bredikhin, Prime number
R. P. Brent, Primality testing and integer factorization
J. Britton, Prime Number List
D. Butler, The first 2000 Prime Numbers
C. K. Caldwell, The Prime Pages
C. K. Caldwell, Tables of primes
C. K. Caldwell, The first 10000 primes
C. K. Caldwell, The first 50,000,000 primes in batches of 1,000,000 (Primes up to 982,451,653.)
C. K. Caldwell, A Primality Test
C. K. Caldwell and Y. Xiong, What is the smallest prime?, J. Integer Seq. 15 (2012), no. 9, Article 12.9.7 and arXiv:1209.2007 [math.HO], 2012.
Chris K. Caldwell, Angela Reddick, Yeng Xiong and Wilfrid Keller, The History of the Primality of One: A Selection of Sources, Journal of Integer Sequences, Vol. 15 (2012), #12.9.8.
M. Chamness, Prime number generator (Applet)
P. Cox, Primes is in P
P. J. Davis & R. Hersh, The Mathematical Experience, The Prime Number Theorem
J.M. De Koninck, Les nombres premiers: mysteres et consolation
J.M. De Koninck, Nombres premiers: mysteres et enjeux
J.P. Delahaye, Formules et nombres premiers
U. Dudley, Formulas for primes, Math. Mag., 56 (1983), 1722.
Pierre Dusart, Autour de la fonction qui compte le nombre de nombres premiers, Thèse, Université de Limoges, France, (1998).
Pierre Dusart, The kth prime is greater than k(ln k + ln ln k1) for k>=2, Mathematics of Computation 68: (1999), 411415.
J. Elie, L'algorithme AKS ou Les nombres premiers sont de classe P
L. Euler, Observations on a theorem of Fermat and others on looking at prime numbers, arXiv:math/0501118 [math.HO], 20052008.
W. Fendt, Table of Primes from 1 to 1000000000000
P. Flajolet, S. Gerhold and B. Salvy, On the nonholonomic character of logarithms, powers and the nth prime function, arXiv:math/0501379 [math.CO], 2005.
J. Flamant, Primes up to one million
K. Ford, Expositions of the PRIMES is in P theorem.
L. & Y. Gallot, The Chronology of Prime Number Records
P. Garrett, Big Primes, Factoring Big Integers
P. Garrett, Naive Primality Test
P. Garrett, Listing Primes
N. Gast, PRIMES is in P: Manindra Agrawal, Neeraj Kayal and Nitin Saxena (in French)
D. A. Goldston, S. W. Graham, J. Pintz and C. Y. Yildirim, Small gaps between primes and almost primes, arXiv:math/0506067 [math.NT], 2005.
A. Granville, It is easy to determine whether a given integer is prime [alternate link]
P. Hartmann, Prime number proofs (in German)
Haskell Wiki, Prime Numbers
ICON Project, List of first 50000 primes grouped within ten columns
James P. Jones, Daihachiro Sato, Hideo Wada and Douglas Wiens, Diophantine representation of the set of prime numbers, The American Mathematical Monthly 83, no. 6 (1976): 449464. DOI: 10.2307/2318339.
N. Kayal & N. Saxena, Resonance 112002, A polynomial time algorithm to test if a number is prime or not
E. Landau, Handbuch der Lehre von der Verteilung der Primzahlen, vol. 1 and vol. 2, Leipzig, Berlin, B. G. Teubner, 1909.
W. Liang & H. Yan, Pseudo Random test of prime numbers, arXiv:math/0603450 [math.NT], 2006.
J. Malkevitch, Primes
Mathworld Headline News, Primality Testing is Easy
K. Matthews, Generating prime numbers
Y. Motohashi, Prime numbersyour gems, arXiv:math/0512143 [math.HO], 2005.
J. Moyer, Some Prime Numbers
C. W. Neville, New Results on Primes from an Old Proof of Euler's, arXiv:math/0210282 [math.NT], 20022003.
L. C. Noll, Prime numbers, Mersenne Primes, Perfect Numbers, etc.
M. A. Nyblom and C. Evans, On the enumeration of partitions with summands in arithmetic progression, Australasian Journal of Combinatorics, Vol. 28 (2003), pp. 149159.
J. J. O'Connor & E. F. Robertson, Prime Numbers
M. E. O'Neill, The Genuine Sieve of Eratosthenes, J. of Functional Programming, Vol 19 Issue 1, Jan 2009, p. 95ff, CUP NY
M. Ogihara & S. Radziszowski, AgrawalKayalSaxena Algorithm for Testing Primality in Polynomial Time
P. Papaphilippou, Plotter of prime numbers frequency graph (flash object) [From Philippos Papaphilippou (philippos(AT)safemail.net), Jun 02 2010]
J. M. Parganin, Primes less than 50000
Ed Pegg, Jr., Sequence Pictures, Math Games column, Dec 08 2003.
Ed Pegg, Jr., Sequence Pictures, Math Games column, Dec 08 2003 [Cached copy, with permission (pdf only)]
I. Peterson, Prime Pursuits
Omar E. Pol, Illustration of initial terms
Omar E. Pol, Sobre el patrón de los números primos, and from Jason Davies, An interactive companion (for primes 2..997)
Popular Computing (Calabasas, CA), Sieves: Problem 43, Vol. 2 (No. 13, Apr 1974), pp. 67. [Annotated and scanned copy]
Primefan, The First 500 Prime Numbers
Primefan, Script to Calculate Prime Numbers
Project Gutenberg Etext, First 100,000 Prime Numbers
C. D. Pruitt, Formulae for Generating All Prime Numbers
R. Ramachandran, Frontline 19 (17) 082000, A Prime Solution
W. S. Renwick, EDSAC log.
F. Richman, Generating primes by the sieve of Eratosthenes
Barkley Rosser, Explicit Bounds for Some Functions of Prime Numbers, American Journal of Mathematics 63 (1941) 211232.
J. Barkley Rosser and Lowell Schoenfeld, Approximate formulas for some functions of prime numbers, Illinois J. Math. Volume 6, Issue 1 (1962), 6494.
S. M. Ruiz and J. Sondow, Formulas for pi(n) and the nth prime, arXiv:math/0210312 [math.NT], 20022014.
S. O. S. Math, First 1000 Prime Numbers
A. Schulman, Prime Number Calculator
M. Slone, PlanetMath.Org, First thousand positive prime numbers
A. Stiglic, The PRIMES is in P little FAQ
ZhiWei Sun, On functions taking only prime values, J. Number Theory, 133 (2013), no. 8, 27942812.
ZhiWei Sun, A conjecture on unit fractions involving primes, Preprint 2015.
Tomas Svoboda, List of primes up to 10^6 [Slow link]
J. Teitelbaum, Review of "Prime numbers:A computational perspective" by R. Crandall & C. Pomerance
J. Thonnard, Les nombres premiers(Primality check; Closest next prime; Factorizer)
J. Tramu, Movie of primes scrolling
A. Turpel, Aesthetics of the Prime Sequence [broken link ?]
S. Wagon, Prime Time: Review of "Prime Numbers:A Computational Perspective" by R. Crandall & C. Pomerance
M. R. Watkins, unusual and physical methods for finding prime numbers
S. Wedeniwski, Primality Tests on Commutator Curves
E. Wegrzynowski, Les formules simples qui donnent des nombres premiers en grande quantites
Eric Weisstein's World of Mathematics, Prime Number.
Eric Weisstein's World of Mathematics, PrimeGenerating Polynomial
Eric Weisstein's World of Mathematics, Prime Spiral
Wikipedia, Prime number
G. Xiao, Primes server, Sequential Batches Primes Listing (up to orders not exceeding 10^308)
G. Xiao, Numerical Calculator, To display p(n) for n up to 41561, operate on "prime(n)"
Index entries for "core" sequences


FORMULA

The prime number theorem is the statement that a(n) ~ n * log n as n > infinity (Hardy and Wright, page 10).
For n >= 2, n*(log n + log log n  3/2) < a(n); for n >= 20, a(n) < n*(log n + log log n  1/2). [Rosser and Schoenfeld]
For all n, a(n) > n log n. [Rosser]
n log(n) + n (log log n  1) < a(n) < n log n + n log log n for n >= 6 [Dusart, quoted in the Wikipedia article]
a(n) = n log n + n log log n + (n/log n)*(log log n  log 2  2) + O( n (log log n)^2/ (log n)^2). [Cipoli, quoted in the Wikipedia article]
a(n) = 2 + sum_{k = 2..floor(2n*log(n)+2)} (1floor(pi(k)/n)), for n > 1, where the formula for pi(k) is given in A000720 (Ruiz and Sondow 2002).  Jonathan Sondow, Mar 06 2004
I conjecture that Sum(1/(p(i)*log(p(i)))) = Pi/2 = 1.570796327... Sum_{i = 1..100000}(1/(p(i)*log(p(i)))) = 1.565585514... It converges very slowly.  Miklos Kristof, Feb 12 2007
The last conjecture has been discussed by the math.research newsgroup recently. The sum, which is greater than Pi/2, is shown in sequence A137245.  T. D. Noe, Jan 13 2009
A000005(a(n)) = 2; A002033(a(n+1)) = 1.  JuriStepan Gerasimov, Oct 17 2009
A001222(a(n)) = 1.  JuriStepan Gerasimov, Nov 10 2009
From Gary Detlefs, Sep 10 2010: (Start)
Conjecture:
a(n) = {n n! mod n^2 = n(n1)}, n <> 4.
a(n) = {n n!*h(n) mod n = n1}, n<>4, where h(n) = sum(1/k, k=1..n). (End)
First 15 primes; a(n) = p + abs(p3/2) + 1/2, where p = m + int((m3)/2), and m = n + int((n2)/8) + int((n4)/8), 1<=n<=15.  Timothy Hopper, Oct 23 2010
a(2n) <= A104272(n)  2 for n > 1, and a(2n) ~ A104272(n) as n > infinity.  Jonathan Sondow, Dec 16 2013
Conjecture: Sequence = {5 and n <> 5 ( Fibonacci(n) mod n = 1 or Fibonacci(n) mod n = n  1) and 2^(n1) mod n = 1}.  Gary Detlefs, May 25 2014
Conjecture: Sequence = {5 and n <> 5 ( Fibonacci(n) mod n = 1 or Fibonacci(n) mod n = n  1) and 2^(3*n) mod 3*n = 8}.  Gary Detlefs, May 28 2014
a(n) = 1 + Sum_{m=1..L(n)}(abs(nPi(m))abs(nPi(m)1/2)+1/2), where Pi(m) = A000720(m) and L(n) >= a(n)1. L(n) can be any function of n which satisfies the inequality. For instance L(n) can be ceil((n+1)*log((n+1)*log(n+1))) since it satisfies this inequality.  Timothy Hopper, May 30 2015, Jun 16 2015
Sum_{n>=1} 1/a(n)^s = P(s), where P(s) is the prime zeta function.  Eric W. Weisstein, Nov 08 2016


MAPLE

A000040 := n>ithprime(n); [ seq(ithprime(i), i=1..100) ];


MATHEMATICA

Prime[Range[60]]
primitiveElements[lst_List] := Block[{lsu = {lst[[1]]}, lsv = Rest@ lst}, While[ Length@ lsv > 0, If [Min@ Mod[ lsv[[1]], lsu] != 0, AppendTo[ lsu, lsv[[1]] ]]; lsv = Rest@ lsv]; lsu]; primitiveElements[ Range[2, 275]] (* or *)
NestList[ NextPrime, 2, 57] (* Robert G. Wilson v, Aug 16 2014 *)


PROG

(MAGMA) [n : n in [2..500]  IsPrime(n)];
(MAGMA) a := func< n  NthPrime(n) >;
(PARI) {a(n) = if( n<1, 0, prime(n))};
(Sage) a = sloane.A000040; print a
print a.list(58) # Jaap Spies, 2007
(Sage) prime_range(1, 300) # Zerinvary Lajos, May 27 2009
(Maxima) A000040(n) := block(
if n = 1 then return(2),
return( next_prime(A000040(n1)))
)$ /* recursive, to be replaced if possible  R. J. Mathar, Feb 27 2012 */
From M. F. Hasler, Oct 21 2013: (Start) The following PARI code provides asymptotic approximations, one based on the asymptotic formula cited above (slight overestimate for n > 10^8), the other one based on pi(x) ~ li(x) = Ei(log(x)) (slight underestimate):
(PARI) prime1(n)=n*(log(n)+log(log(n))1+(log(log(n))2)/log(n)((log(log(n))6)*log(log(n))+11)/log(n)^2/2)
(PARI) prime2(n)=solve(X=n*log(n)/2, 2*n*log(n), real(eint1(log(X)))+n) \\ (End)
(Haskell) See also Haskell Wiki Link
import Data.List (genericIndex)
a000040 n = genericIndex a000040_list (n  1)
a000040_list = base ++ larger where
base = [2, 3, 5, 7, 11, 13, 17]
larger = p : filter prime more
prime n = all ((> 0) . mod n) $ takeWhile (\x > x*x <= n) larger
_ : p : more = roll $ makeWheels base
roll (Wheel n rs) = [n * k + r  k < [0..], r < rs]
makeWheels = foldl nextSize (Wheel 1 [1])
nextSize (Wheel size bs) p = Wheel (size * p)
[r  k < [0..p1], b < bs, let r = size*k+b, mod r p > 0]
data Wheel = Wheel Integer [Integer]
 Reinhard Zumkeller, Apr 07 2014
(PARI) forprime(p=2, 10^3, print1(p, ", ")) \\ Felix Fröhlich, Jun 30 2014


CROSSREFS

Cf. A002808, A008578, A006879, A006880, A000720 ("pi"), A001223 (differences between primes), A233588.
Cf. primes in lexicographic order: A210757, A210758, A210759, A210760, A210761.
Cf. A003558, A179480 (relating to the Quasiorder theorem of Hilton and Pedersen).
Boustrophedon transforms: A000747, A000732, A230953.
a(2n) = A104272(n)  A233739(n).
Cf. A002476, A003627.
Sequence in context: A216884 A216885 A216886 A273960 A100726 A015919 A064555
Adjacent sequences: A000037 A000038 A000039 * A000041 A000042 A000043


KEYWORD

core,nonn,nice,easy,changed


AUTHOR

N. J. A. Sloane, Apr 30 1991


STATUS

approved



