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A187419 Least odd prime p such that p*2^(2^n)+1 is prime. 1
3, 3, 7, 3, 37, 43, 163, 1171, 607, 223, 1987, 3541, 23917, 43627, 8887, 108517, 1063, 378667 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..17.

PROG

PFGW SCRIPTIFY

SCRIPT

DIM nn, -1

DIM kk

DIMS tt

LABEL loopn

SET nn, nn+1

SET kk, 1

LABEL loopk

SET kk, kk+1

SETS tt, %d, %d, %d\,; nn; kk; p(kk)

PRP p(kk)*2^(2^nn)+1, tt

IF ISPRIME THEN GOTO loopn

IF ISPRP THEN GOTO loopn

GOTO loopk

(PARI) A187419(n)={

        local(f =2^(2^n), p=3);

        while(1,

                if(isprime(f*p+1),

                        return(p)

                );

                p=nextprime(p+1);

        ) ;

} /* R. J. Mathar, Mar 11 2011 */

CROSSREFS

Cf. A187088.

Sequence in context: A100587 A324548 A249383 * A099282 A002937 A085870

Adjacent sequences:  A187416 A187417 A187418 * A187420 A187421 A187422

KEYWORD

nonn,hard

AUTHOR

Pierre CAMI, Mar 09 2011

STATUS

approved

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Last modified February 18 21:20 EST 2020. Contains 332028 sequences. (Running on oeis4.)