A187419 Least odd prime p such that p*2^(2^n)+1 is prime.

3, 3, 7, 3, 37, 43, 163, 1171, 607, 223, 1987, 3541, 23917, 43627, 8887, 108517, 1063, 378667

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