A143393 a(n) is the least prime p such that p*(p+prime(n))-1 is prime with prime(i)=i-th prime.

2, 3, 2, 2, 3, 2, 2, 2, 5, 2, 3, 7, 3, 2, 2, 2, 7, 3, 2, 5, 2, 5, 3, 2, 2, 3, 3, 7, 5, 2, 2, 3, 2, 2, 5, 3, 2, 5, 2, 2, 5, 5, 11, 2, 2, 2, 3, 2, 2, 2, 11, 7, 5, 3, 7, 3, 2, 3, 2, 5, 2, 3, 2, 3, 3, 5, 11, 2, 3, 2, 2, 29, 3, 5, 2, 2, 37, 2, 5, 2, 11, 5, 3, 3, 2, 5, 5, 5, 23, 2, 2, 17, 2, 3, 7, 2, 2, 3, 2, 5, 2, 2

Offset

1,1

Links

Pierre CAMI, Table of n, a(n) for n = 1..12250

Example

2*(2+2)-1=7 prime so a(1)=2 as prime(1)=2;
2*(2+3)-1=9 composite; 3*(3+3)-1=17 prime so a(2)=3 as prime(2)=3.

Prog

(PARI) a(n) = {my(pn=prime(n), p=2); while (!isprime(p*(p+pn)-1), p = nextprime(p+1)); p; } \\ Michel Marcus, Sep 24 2019

Crossrefs

Cf. A143394.

Sequence in context: A128049 A104543 A054988 * A269111 A166497 A116909

Adjacent sequences: A143390 A143391 A143392 * A143394 A143395 A143396

Keyword

nonn

Author

Pierre CAMI, Aug 12 2008

Extensions

Name edited by Michel Marcus, Sep 24 2019

Status

approved