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Search: id:A006992
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| A006992 |
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Bertrand primes: a(n) is largest prime < 2*a(n-1).
(Formerly M0675)
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+0
27
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| 2, 3, 5, 7, 13, 23, 43, 83, 163, 317, 631, 1259, 2503, 5003, 9973, 19937, 39869, 79699, 159389, 318751, 637499, 1274989, 2549951, 5099893, 10199767, 20399531, 40799041, 81598067, 163196129, 326392249, 652784471, 1305568919, 2611137817
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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M. Aigner and G. M. Ziegler, Proofs from The Book, Springer-Verlag, Berlin, 1999; see p. 7.
M. Griffiths, The Backbone of Pascal's Triangle, United Kingdom Mathematics Trust (2008), page 115. [From Martin Griffiths (griffm(AT)essex.ac.uk), Mar 28 2009]
G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, p. 344.
I. Niven and H. S. Zuckerman, An Introduction to the Theory of Numbers. 2nd ed., Wiley, NY, 1966, p. 189.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..100
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MAPLE
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A006992 := proc(n) option remember; if n=1 then 2 else prevprime(2*A006992(n-1)); fi; end;
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MATHEMATICA
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PrevPrime[ n_Integer ] := Module[ {k}, k = n - 1; While[ ! PrimeQ[ k ], k-- ]; k ]; a[ 1 ] = 2; a[ n_ ] := PrevPrime[ 2*a[ n - 1 ] ]; Table[ a[ n ], {n, 1, 40} ]
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CROSSREFS
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Cf. A055496.
Cf. also A163961 [From Vladimir Shevelev (shevelev(AT)bgu.ac.il), Aug 07 2009]
Sequence in context: A064336 A126092 A132394 this_sequence A080190 A076994 A124147
Adjacent sequences: A006989 A006990 A006991 this_sequence A006993 A006994 A006995
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com)
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