A126990 Largest prime preceding geometric mean of prime(n) and prime(n+2).

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

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

Amiram Eldar, Table of n, a(n) for n = 1..10000

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

Cf. A007917, A073273.

Sequence in context: A336416 A128508 A083743 * A128498 A146906 A147449

Adjacent sequences: A126987 A126988 A126989 * A126991 A126992 A126993

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