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Search: id:A126990
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| A126990 |
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Largest prime preceding geometric mean of prime(n-1) and prime(n+1). |
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+0
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
(list; graph; listen)
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OFFSET
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2,1
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COMMENT
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With duplicates removed, seems to be a subsequence of A105399 and A105792. (M. F. Hasler, Jun 14 2007)
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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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MATHEMATICA
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<< NumberTheory`NumberTheoryFunctions` a = {}; Do[AppendTo[a, PreviousPrime[Sqrt[(Prime[x - 1])*(Prime[x + 1])]]], {x, 2, 100}]; a
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PROGRAM
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(PARI) A126990(n)={ n=sqrtint(prime(n-1)*prime(n+1)); if( 0==n%2, n--); while(!isprime(n), n-=2); n } /* then vector(50, n, A126990(n+1)) displays a list of values */ - M. F. Hasler, Jun 14 2007
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CROSSREFS
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Sequence in context: A109580 A128508 A083743 this_sequence A128498 A146906 A147449
Adjacent sequences: A126987 A126988 A126989 this_sequence A126991 A126992 A126993
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KEYWORD
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nonn
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AUTHOR
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Artur Jasinski (grafix(AT)csl.pl), Jan 01 2007
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EXTENSIONS
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Edited by M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Jun 14 2007
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