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A060715
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Number of primes between n and 2n exclusive.
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42
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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, 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, 12, 12, 12, 13, 13, 14, 13, 13, 14, 15, 14, 14, 13, 13, 14, 15, 15
(list;
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refs;
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history;
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OFFSET
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1,4
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COMMENTS
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See the additional references and links mentioned in A143227. [Jonathan Sondow, Aug 03 2008]
a(A060756(n)) = n and a(m) <> n for m < A060756(n). [Reinhard Zumkeller, Jan 08 2012]
For prime n conjecturally a(n) = A226859(n). [Vladimir Shevelev, Jun 27 2013]
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]
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REFERENCES
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M. Aigner and C. M. Ziegler, Proofs from The Book, Chapter 2, Springer NY 2001.
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LINKS
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T. D. Noe, Table of n, a(n) for n = 1..1000
C. K. Caldwell, The Prime Glossary, Bertrand's postulate
R. Chapman, Bertrand postulate [Broken link]
Math Olympiads, Bertrand's Postulate [Broken link]
S. Ramanujan, A proof of Bertrand's postulate, J. Indian Math. Soc., 11 (1919), 181-182.
V. Shevelev, Ramanujan and Labos Primes, Their Generalizations, and Classifications of Primes, arXiv:0909.0715v13 [math.NT]
V. Shevelev, Ramanujan and Labos Primes, Their Generalizations, and Classifications of Primes, Journal of Integer Sequences, Vol. 15 (2012), Article 12.5.4
M. Slone, PlanetMath.org, Proof of Bertrand's conjecture
J. Sondow and Eric Weisstein, Bertrand's Postulate, World of Mathematics
Wikipedia, Proof of Bertrand's postulate
Dr. Wilkinson, The Math Forum, Erdos' Proof
Wolfram Research, Bertrand hypothesis
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FORMULA
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a(n) = sum(A010051(n+k): 1<=k<n). [Reinhard Zumkeller, Dec 03 2009]
a(n) = A000720(2n-1) - A000720(n). [Wesley Ivan Hurt, Aug 21 2013]
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EXAMPLE
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a(35)=8 since eight consecutive primes (37,41,43,47,53,59,61,67) are located between 35 and 70.
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MAPLE
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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:
with(numtheory); seq(pi(2*k-1)-pi(k), k=1..100); #[Wesley Ivan Hurt, Aug 21 2013]
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MATHEMATICA
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a[n_]:=PrimePi[2n-1]-PrimePi[n]; Table[a[n], {n, 1, 84}] (* Jean-François Alcover, Mar 20 2011 *)
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PROG
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(PARI) { for (n=1, 1000, write("b060715.txt", n, " ", primepi(2*n - 1) - primepi(n)); ) } [From Harry J. Smith, Jul 10 2009]
(Haskell)
a060715 n = sum $ map a010051 [n+1..2*n-1] -- Reinhard Zumkeller, Jan 08 2012
(MAGMA) [0] cat [#PrimesInInterval(n+1, 2*n-1): n in [2..80]]; // Bruno Berselli, Sep 05 2012
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CROSSREFS
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Cf. A060756, A070046, A006992, A051501, A035250, A101909.
Cf. A000720, A014085, A104272, A143223-A143227.
Sequence in context: A114920 A283190 A030361 * A108954 A123920 A029170
Adjacent sequences: A060712 A060713 A060714 * A060716 A060717 A060718
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KEYWORD
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nonn,easy
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AUTHOR
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Lekraj Beedassy, Apr 25 2001
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EXTENSIONS
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Corrected by Dug Eichelberger (dug(AT)mit.edu), Jun 04 2001.
More terms from Larry Reeves (larryr(AT)acm.org), Jun 05 2001
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STATUS
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approved
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