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URL: https://oeis.org/A129786

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A129786
Least k such that 2^(2^n)+k is prime.
2
0, 1, 1, 1, 1, 15, 13, 51, 297, 75, 643, 981, 1761, 897, 2775, 118113, 44061, 5851, 18531, 189093, 69661
OFFSET
0,6
COMMENTS
It is conjectured that a(n)>=3 for n>=5.
For n>11, 2^(2^n)+a(n) is a probable prime. By a comment in A000215, a(n) is not 2^m+1 for any m > 1. - T. D. Noe, Jul 19 2007
LINKS
C. K. Caldwell, The Prime Glossary, Fermat prime.
Eric Weisstein's World of Mathematics, Fermat Number.
Eric Weisstein's World of Mathematics, Fermat Prime.
MATHEMATICA
a[n_] := Module[{k = 0}, While[! PrimeQ[2^(2^n) + k], k++]; k]; Array[a, 12, 0] (* Amiram Eldar, Jun 11 2022 *)
PROG
(PARI) a(n)=if(n<0, 0, s=0; while(isprime(2^(2^n)+s)==0, s++); s)
(Python)
from sympy import nextprime
def a(n): m = 2**(2**n); return nextprime(m-1) - m
print([a(n) for n in range(12)]) # Michael S. Branicky, Jun 12 2022
CROSSREFS
Cf. A013597 (least k>0 such that 2^n+k is prime).
Sequence in context: A299315 A072348 A317422 * A104056 A131285 A130677
KEYWORD
nonn,more
AUTHOR
Benoit Cloitre, May 18 2007
EXTENSIONS
More terms from T. D. Noe, Jul 19 2007
a(18)-a(19) by Makoto Morimoto, added by Boyan Hu, Jul 05 2025
a(20) by Boyan Hu, Jul 05 2025
STATUS
approved