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A006990
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Largest prime <= n!.
(Formerly M1541)
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18
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2, 5, 23, 113, 719, 5039, 40289, 362867, 3628789, 39916787, 479001599, 6227020777, 87178291199, 1307674367953, 20922789887947, 355687428095941, 6402373705727959, 121645100408831899, 2432902008176639969, 51090942171709439969, 1124000727777607679927
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OFFSET
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2,1
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COMMENTS
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Conjecture: For n >= 2, n! - a(n) is 1 or a prime, see A033933. - Amarnath Murthy, Mar 19 2002
a(n) is the largest prime divisor of (n!)! of the sequence A000197. - Stanislav Sykora, Jul 14 2014
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REFERENCES
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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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Donovan Johnson, Table of n, a(n) for n = 2..400
R. G. Wilson v, Letter to N. J. A. Sloane, Oct. 1993
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MATHEMATICA
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PrevPrime[ n_Integer ] := Module[ {k = n - 1}, While[ ! PrimeQ[ k ], k-- ]; k ]; Table[ PrevPrime[ n! ], {n, 3, 25} ]
Join[{2}, NextPrime[Range[3, 30]!, -1]] (* Harvey P. Dale, Jan 24 2014 *)
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CROSSREFS
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Cf. A000142, A007917.
Sequence in context: A279819 A249606 A003501 * A358608 A242227 A032182
Adjacent sequences: A006987 A006988 A006989 * A006991 A006992 A006993
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane, Robert G. Wilson v
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EXTENSIONS
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More terms from Jud McCranie; also from Robert G. Wilson v, Jan 03 2001
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STATUS
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approved
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