A051686 - OEIS

A051686

Smallest prime p such that 2n*p+1 is also prime.

2, 3, 2, 2, 3, 3, 2, 7, 2, 2, 3, 3, 2, 7, 2, 3, 3, 2, 5, 7, 3, 2, 3, 2, 2, 3, 2, 2, 19, 3, 5, 3, 3, 2, 3, 13, 2, 3, 2, 3, 19, 5, 2, 7, 2, 3, 3, 2, 2, 7, 3, 3, 7, 5, 3, 3, 2, 2, 7, 2, 3, 3, 3, 2, 7, 3, 2, 3, 2, 2, 13, 3, 2, 37, 5, 3, 3, 2, 2, 13, 3, 5, 3, 2, 11, 13, 2, 2, 31, 3, 3, 7, 2, 5, 3, 3, 2, 7, 2, 2

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

These are the primes arising in A051899.

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

EXAMPLE

a(29)=19 because 19 is the smallest prime p such that 2*29*p+1 is prime.

MATHEMATICA

Table[k = 1; While[! PrimeQ[2 n Prime@ k + 1], k++]; Prime@ k, {n, 120}] (* Michael De Vlieger, Jul 26 2016 *)

PROG