OFFSET
0,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..1000
FORMULA
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 *)
PROG
(Python)
from sympy import prevprime, nextprime
def A117387(n): return (m if (m:=nextprime(k:=1<<n)) < (k<<1)-(r:=prevprime(k)) else r) if n>1 else 2 # Chai Wah Wu, Aug 08 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Lekraj Beedassy, Mar 11 2006
EXTENSIONS
Edited, corrected and extended by Robert G. Wilson v, Mar 14 2006
STATUS
approved