A090808 Numbers n such that numerator(sum(i=1,n, prime(i)/prime(i+1))) is prime.

1, 2, 4, 14, 22, 48, 52, 88, 310, 796

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