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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
| 1,2
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EXAMPLE
| 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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PROG
| (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
| Sequence in context: A071865 A127596 A111871 * A074716 A090889 A096012
Adjacent sequences: A090805 A090806 A090807 * A090809 A090810 A090811
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KEYWORD
| hard,nonn
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AUTHOR
| mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 16 2004
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