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A117387 Prime nearest to 2^n. In case of a tie, choose the smaller. 8
2, 2, 3, 7, 17, 31, 61, 127, 257, 509, 1021, 2053, 4093, 8191, 16381, 32771, 65537, 131071, 262147, 524287, 1048573, 2097143, 4194301, 8388617, 16777213, 33554467, 67108859, 134217757, 268435459, 536870909, 1073741827, 2147483647 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 0..1000

FORMULA

a(n) = A000079(n) + A059959(n).

MATHEMATICA

f[n_] := Block[{k = 0}, While[ !PrimeQ[2^n - k] && !PrimeQ[2^n + k], k++ ]; Min@Select[{2^n - k, 2^n + k}, PrimeQ@# &]]

pn2n[n_]:=Module[{c=2^n, a, b}, a=NextPrime[c, -1]; b=NextPrime[c]; If[b-c < c-a, b, a]]; Join[{2, 2}, Table[pn2n[n], {n, 2, 40}]] (* Harvey P. Dale, Jul 24 2019 *)

CROSSREFS

Sequence in context: A038075 A032236 A128776 * A113842 A032161 A265801

Adjacent sequences:  A117384 A117385 A117386 * A117388 A117389 A117390

KEYWORD

nonn

AUTHOR

Lekraj Beedassy, Mar 11 2006

EXTENSIONS

Edited, corrected and extended by Robert G. Wilson v, Mar 14 2006

STATUS

approved

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Last modified August 23 00:50 EDT 2019. Contains 326211 sequences. (Running on oeis4.)