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A071194 Length (>1) of shortest sequence of consecutive primes starting with prime(n) whose sum is also prime, or -1 if no such sequence exists. 7
2, 9, 3, 3, 3, 5, 3, 3, 3, 3, 3, 9, 3, 5, 7, 3, 5, 3, 3, 3, 5, 3, 3, 7, 7, 3, 7, 5, 3, 5, 5, 9, 5, 3, 3, 5, 3, 3, 11, 9, 5, 21, 5, 9, 3, 9, 3, 5, 55, 3, 7, 27, 9, 27, 7, 5, 5, 3, 9, 3, 3, 3, 5, 3, 7, 7, 11, 3, 3, 3, 5, 5, 7, 7, 3, 5, 3, 9, 3, 3, 5, 11, 3, 5, 47, 5, 3, 3, 5, 3, 3, 5, 7, 3, 3, 7, 3, 5, 5, 5, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=1, start-prime = prime(1) = 2, 2+3=5 is prime, length=2, so a(1)=2;
for n=2, start-prime = prime(2) = 3, 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 + 29 = 127 is prime, length=9, all shorter partial sums are composite, so a(2)=9;
for n=160, prime(160) = 941, 941 + ... + 1609 = 121123 is prime, a(160)=95.
MATHEMATICA
Table[k = 2; While[CompositeQ@ Total@ Prime@ Range[n, n + k], k++]; k + 2 Boole[EvenQ@ k] - 1, {n, 120}] (* Michael De Vlieger, Jan 01 2017 *)
PROG
(PARI) a(n, p=prime(n))=my(q=p, t=2); while(!isprime(p+=q=nextprime(q+1)), t++); t
apply(p->a(0, p), primes(30)) \\ Charles R Greathouse IV, Jun 16 2015
CROSSREFS
Sequence in context: A011240 A021345 A011066 * A347359 A346839 A137616
KEYWORD
nonn
AUTHOR
Labos Elemer, May 16 2002
EXTENSIONS
Escape clause added by N. J. A. Sloane, Nov 17 2020
STATUS
approved

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Last modified May 22 06:48 EDT 2024. Contains 372743 sequences. (Running on oeis4.)