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Search: id:A124247
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| A124247 |
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Numbers n such that n!!-8 and n!!+8 are two consecutive primes. |
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OFFSET
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1,1
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COMMENT
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n is in the sequence iff n!!-8 and n!!+8 are primes and the four numbers n!!-2,n!!+2, n!!-4 & n!!+4 are composites. It's interesting that related to the term 341 we can say 341!!-(3+4+1) and 341!!+(3+4+1) are two consecutive primes with length 341+prime(3+4+1). Conjecture: 341 is the largest term of this sequence.
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EXAMPLE
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341 is in the sequence because 341!!-8 and 341!!+8 are primes and the four numbers 341!!-2, 341!!+2, 341!!-4 & 341!!+4 are composites.
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MATHEMATICA
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Select[Range[5, 500], PrimeQ[ #!!-8]&&PrimeQ[ #!!+8]&&!PrimeQ[ #!!-4] &&!PrimeQ[ #!!+4]&&!PrimeQ[ #!!-2]&&!PrimeQ[ #!!+2]&]
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CROSSREFS
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Cf. A076188.
Sequence in context: A044179 A044560 A039469 this_sequence A142658 A126588 A142794
Adjacent sequences: A124244 A124245 A124246 this_sequence A124248 A124249 A124250
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KEYWORD
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nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Nov 19 2006
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