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A090808 Numbers n such that numerator(sum(i=1,n, prime(i)/prime(i+1))) is prime. 0
1, 2, 4, 14, 22, 48, 52, 88, 310, 796 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

No more terms up to and including n=2000. - Harvey P. Dale, Dec 16 2018

LINKS

Table of n, a(n) for n=1..10.

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.

MATHEMATICA

Position[Numerator[Accumulate[#[[1]]/#[[2]]&/@Partition[Prime[ Range[ 800]], 2, 1]]], _?(PrimeQ[#]&)]//Flatten (* Harvey P. Dale, Dec 16 2018 *)

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)))

CROSSREFS

Sequence in context: A127596 A111871 A291079 * A074716 A283290 A283379

Adjacent sequences:  A090805 A090806 A090807 * A090809 A090810 A090811

KEYWORD

hard,nonn

AUTHOR

mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 16 2004

STATUS

approved

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Last modified September 16 20:51 EDT 2021. Contains 347473 sequences. (Running on oeis4.)