A071576 a(n) = least k such that 2ik + 1 is prime for all 1 <= i <= n.

1, 1, 1, 165, 5415, 12705, 256410, 256410, 6480303060, 217245863835, 946622690475, 35511547806735, 439116128090640, 5714676453270219435

Offset: 1

Author

Benoit Cloitre, May 31 2002

Keywords

• more
• nonn

Crossrefs

Cf. A088250, A124516, A124522, A124522, A063983.

Cf. A005097, A123998, A124408-A124411.

Programs

Mathematica

k = 1; Do[ While[p = Table[2*i*k + 1, {i, 1, n}]; Union[ PrimeQ[p]] != {True}, k++ ]; Print[k], {n, 1, 15}] (* Robert G. Wilson v *)

PARI

for(n=1,6,s=1; while(sum(i=1,n,isprime(2*s*i+1))
				

Extensions

Extended by Robert G. Wilson v, Jun 06 2002

a(9) from Ryan Propper, Jun 20 2005

a(10)-a(13) from Don Reble, Nov 05 2006

a(14) from Giovanni Resta, Apr 01 2017