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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 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.)