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A126990 Largest prime preceding geometric mean of prime(n) and prime(n+2). 6
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; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
With duplicates removed, seems to be a subsequence of A105399 and A105792. - M. F. Hasler, Jun 14 2007
REFERENCES
P. Ribenboim, The Little Book of Bigger Primes, Springer-Verlag NY 2004.
LINKS
FORMULA
a(n) = A007917(A073273(n)). - Michel Marcus, Nov 07 2013
MATHEMATICA
<< NumberTheory`NumberTheoryFunctions` a = {}; Do[AppendTo[a, PreviousPrime[Sqrt[(Prime[x])*(Prime[x + 2])]]], {x, 1, 100}]; a
PROG
(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
CROSSREFS
Sequence in context: A336416 A128508 A083743 * A128498 A146906 A147449
KEYWORD
nonn
AUTHOR
Artur Jasinski, Jan 01 2007
EXTENSIONS
Edited by M. F. Hasler, Jun 14 2007
Definition changed so that offset is now 1 by Michel Marcus, Nov 07 2013
STATUS
approved

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)