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A090808
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Numbers n such that numerator(sum(i=1,n, prime(i)/prime(i+1))) is prime.
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0
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OFFSET
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1,2
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COMMENTS
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No more terms up to and including n=2000. - Harvey P. Dale, Dec 16 2018
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LINKS
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EXAMPLE
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a(2)=2 2/3 + 3/5 = 19/15 and 19 is prime and prime(2+1)=5.
a(3)=4 because 2/3+3/5+5/7+7/11 = 3023/1155 and 3023 is prime and prime(4+1)=11.
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MATHEMATICA
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Position[Numerator[Accumulate[#[[1]]/#[[2]]&/@Partition[Prime[ Range[ 800]], 2, 1]]], _?(PrimeQ[#]&)]//Flatten (* Harvey P. Dale, Dec 16 2018 *)
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PROG
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(PARI) pp(n)= s=0; for (i=1, n, s=s+prime(i)/prime(i+1)); return(s); for (i=1, 800, if(isprime(numerator(pp(i))), print(i)))
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CROSSREFS
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KEYWORD
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hard,nonn
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AUTHOR
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mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 16 2004
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STATUS
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approved
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