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A090808

Numbers m such that the numerator of Sum_{i=1..m} prime(i)/prime(i+1) is prime.

1, 2, 4, 14, 22, 48, 52, 88, 310, 796, 5688, 6422

OFFSET

1,2

LINKS

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))), print1(i, ", ")))

CROSSREFS

KEYWORD

nonn,hard,more

AUTHOR

Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Feb 16 2004

EXTENSIONS

a(11)-a(12) from Michael S. Branicky, Aug 27 2024

STATUS

approved

URL: https://oeis.org/A090808