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A126990
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Largest prime preceding geometric mean of prime(n) and prime(n+2).
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6
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3, 3, 7, 7, 13, 13, 19, 23, 23, 31, 31, 37, 43, 47, 47, 53, 61, 61, 67, 73, 73, 83, 89, 89, 97, 103, 103, 109, 113, 113, 131, 131, 139, 139, 151, 151, 157, 167, 167, 173, 181, 181, 193, 193, 199, 199, 211, 223, 229, 233, 233, 241, 241, 251, 257, 263, 271, 271, 277
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OFFSET
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1,1
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COMMENTS
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REFERENCES
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P. Ribenboim, The Little Book of Bigger Primes, Springer-Verlag NY 2004.
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LINKS
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FORMULA
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MATHEMATICA
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<< NumberTheory`NumberTheoryFunctions` a = {}; Do[AppendTo[a, PreviousPrime[Sqrt[(Prime[x])*(Prime[x + 2])]]], {x, 1, 100}]; a
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PROG
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(PARI) A126990(n)={ n=sqrtint(prime(n)*prime(n+2)); if( 0==n%2, n--); while(!isprime(n), n-=2); n } /* then vector(50, n, A126990(n)) displays a list of values, M. F. Hasler, Jun 14 2007 */
(PARI) a(n)= precprime(sqrtint(prime(n)*prime(n+2))); \\ Michel Marcus, Nov 07 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Definition changed so that offset is now 1 by Michel Marcus, Nov 07 2013
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STATUS
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approved
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