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Search: id:A140315
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| A140315 |
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Numbers n such that n!/n#-1 and n!/n#+1 is a probable twin prime pair. |
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+0
1
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OFFSET
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4,1
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COMMENT
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a(4),a(5) and a(280),a(281) result in the same respective twin prime pairs.
a(281) produces 453 digit components. Using gmp, testing n < 4000, the last
3-prp found was the 8897 digit 3-prp, 3337!/3337#-1.
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FORMULA
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n# is the primorial function. We define 0# = 1# = 1.
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EXAMPLE
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8!/8#-1 = 191,8!/8#-1 = 193. 191 and 193 form a twin prime pair.
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PROGRAM
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(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) }
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CROSSREFS
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Sequence in context: A072808 A104884 A113726 this_sequence A055497 A093088 A019637
Adjacent sequences: A140312 A140313 A140314 this_sequence A140316 A140317 A140318
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KEYWORD
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nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)hotmail.com), May 25 2008
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