

A071576


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


11



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

1,4


LINKS

Table of n, a(n) for n=1..14.


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 *)


PROG

(PARI) for(n=1, 6, s=1; while(sum(i=1, n, isprime(2*s*i+1))<n, s++); print1(s, ", "))


CROSSREFS

Cf. A088250, A124516, A124522, A124522, A063983.
Cf. A005097, A123998, A124408A124411.
Sequence in context: A145055 A194483 A105944 * A140912 A132055 A273441
Adjacent sequences: A071573 A071574 A071575 * A071577 A071578 A071579


KEYWORD

more,nonn


AUTHOR

Benoit Cloitre, May 31 2002


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


STATUS

approved



