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A060715 Number of primes between n and 2n exclusive. 38

%I

%S 0,1,1,2,1,2,2,2,3,4,3,4,3,3,4,5,4,4,4,4,5,6,5,6,6,6,7,7,6,7,7,7,7,8,

%T 8,9,9,9,9,10,9,10,9,9,10,10,9,9,10,10,11,12,11,12,13,13,14,14,13,13,

%U 12,12,12,13,13,14,13,13,14,15,14,14,13,13,14,15,15

%N Number of primes between n and 2n exclusive.

%C See the additional references and links mentioned in A143227. [_Jonathan Sondow_, Aug 03 2008]

%C a(A060756(n)) = n and a(m) <> n for m < A060756(n). [_Reinhard Zumkeller_, Jan 08 2012]

%C For prime n conjecturally a(n) = A226859(n). [_Vladimir Shevelev_, Jun 27 2013]

%C The number of partitions of 2n+2 into exactly two parts where the first part is a prime strictly less than 2n+1. [_Wesley Ivan Hurt_, Aug 21 2013]

%D M. Aigner and C. M. Ziegler, Proofs from The Book, Chapter 2, Springer NY 2001.

%H T. D. Noe, <a href="/A060715/b060715.txt">Table of n, a(n) for n = 1..1000</a>

%H C. K. Caldwell, The Prime Glossary, <a href="http://primes.utm.edu/glossary/page.php/Bertrandspostulate.html">Bertrand's postulate</a>

%H R. Chapman, <a href="http://www.maths.ex.ac.uk/~rjc/etc/bertrand.pdf">Bertrand postulate</a> [Broken link]

%H Math Olympiads, <a href="http://matholymp.com/TUTORIALS/Bertrand.pdf">Bertrand's Postulate</a> [Broken link]

%H S. Ramanujan, <a href="http://ramanujan.sirinudi.org/Volumes/published/ram24.html">A proof of Bertrand's postulate</a>, J. Indian Math. Soc., 11 (1919), 181-182.

%H V. Shevelev, <a href="http://arxiv.org/abs/0909.0715">Ramanujan and Labos Primes, Their Generalizations, and Classifications of Primes</a>, arXiv:0909.0715v13 [math.NT]

%H V. Shevelev, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL15/Shevelev/shevelev19.html">Ramanujan and Labos Primes, Their Generalizations, and Classifications of Primes</a>, Journal of Integer Sequences, Vol. 15 (2012), Article 12.5.4

%H M. Slone, PlanetMath.org, <a href="http://planetmath.org/encyclopedia/ProofOfBertrandsConjecture.html">Proof of Bertrand's conjecture</a>

%H J. Sondow and Eric Weisstein, <a href="http://mathworld.wolfram.com/BertrandsPostulate.html">Bertrand's Postulate</a>, World of Mathematics

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Proof_of_Bertrand%27s_postulate">Proof of Bertrand's postulate</a>

%H Dr. Wilkinson, The Math Forum, <a href="http://mathforum.org/library/drmath/view/51527.html">Erdos' Proof</a>

%H Wolfram Research, <a href="http://functions.wolfram.com/NumberTheoryFunctions/Prime/31/03/ShowAll.html">Bertrand hypothesis</a>

%F a(n) = sum(A010051(n+k): 1<=k<n). [_Reinhard Zumkeller_, Dec 03 2009]

%F a(n) = A000720(2n-1) - A000720(n). [_Wesley Ivan Hurt_, Aug 21 2013]

%e a(35)=8 since eight consecutive primes (37,41,43,47,53,59,61,67) are located between 35 and 70.

%p a := proc(n) local counter, i; counter := 0; from i from n+1 to 2*n-1 do if isprime(i) then counter := counter +1; fi; od; return counter; end:

%p with(numtheory); seq(pi(2*k-1)-pi(k),k=1..100); #[_Wesley Ivan Hurt_, Aug 21 2013]

%t a[n_]:=PrimePi[2n-1]-PrimePi[n]; Table[a[n],{n,1,84}] (* _Jean-Fran├žois Alcover_, Mar 20 2011 *)

%o (PARI) { for (n=1, 1000, write("b060715.txt", n, " ", primepi(2*n - 1) - primepi(n)); ) } [From _Harry J. Smith_, Jul 10 2009]

%o (Haskell)

%o a060715 n = sum $ map a010051 [n+1..2*n-1] -- _Reinhard Zumkeller_, Jan 08 2012

%o (MAGMA) [0] cat [#PrimesInInterval(n+1, 2*n-1): n in [2..80]]; // _Bruno Berselli_, Sep 05 2012

%Y Cf. A060756, A070046, A006992, A051501, A035250, A101909.

%Y Cf. A000720, A014085, A104272, A143223-A143227.

%K nonn,easy

%O 1,4

%A _Lekraj Beedassy_, Apr 25 2001

%E Corrected by Dug Eichelberger (dug(AT)mit.edu), Jun 04 2001.

%E More terms from Larry Reeves (larryr(AT)acm.org), Jun 05 2001

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Last modified December 20 15:43 EST 2014. Contains 252266 sequences.