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A140315 Numbers n such that n!/n#-1 and n!/n#+1 is a twin prime pair. 4
4, 5, 8, 34, 280, 281 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,1

COMMENTS

4,5 and 280,281 result in the same respective twin prime pairs. Using gmp, testing n < 4000, the last 3-prp found was the 8897 digit 3-prp, 3337!/3337#-1.

LINKS

Table of n, a(n) for n=4..9.

G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 281

FORMULA

n# is the primorial function A034386(n).

A140293 INTERSECT A140294. - R. J. Mathar, Feb 27 2012

EXAMPLE

8!/8#-1 = 191,8!/8#-1 = 193. 191 and 193 form a twin prime pair.

PROG

(PARI) g(n) = for(x=1, n, y=x!/primorial(x)-1; z=nextprime(y+1); if(ispseudoprime(y)&&z-y==2, print1(x", "))) primorial(n) = \ The product of primes <= n using the pari primelimit. { local(p1, x); if(n==0||n==1, return(1)); p1=1; forprime(x=2, n, p1*=x); return(p1) }

CROSSREFS

Sequence in context: A207191 A240790 A229861 * A055497 A194419 A175380

Adjacent sequences:  A140312 A140313 A140314 * A140316 A140317 A140318

KEYWORD

hard,nonn

AUTHOR

Cino Hilliard, May 25 2008

STATUS

approved

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Last modified April 26 11:46 EDT 2019. Contains 322472 sequences. (Running on oeis4.)