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A056206 Smallest prime p such that p + 2^n is also a prime. 11
2, 3, 3, 3, 3, 5, 3, 3, 7, 11, 7, 5, 3, 17, 37, 3, 3, 29, 3, 53, 7, 17, 67, 11, 43, 41, 97, 29, 3, 11, 3, 11, 61, 17, 79, 53, 31, 29, 7, 23, 97, 71, 277, 29, 7, 59, 127, 5, 61, 191, 193, 101, 37, 5, 163, 3, 97, 131, 577, 131, 151, 197, 193, 29, 13, 131, 709, 3, 61 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000

FORMULA

a(n) = Min{p|p+2^n=q, both p and q are primes}.

EXAMPLE

n=9, 512 + {2,3,5,7,11,...} = {514,515,519,523,...} = {2*257, 5*103, 11*47, 3*173, 523=prime, ...}. The smallest suitable prime is 11 and it gives 523 = 512 + 11. So a(9)=11.

MATHEMATICA

Table[i=1; While[!PrimeQ[2^n+(p=Prime[i])], i++]; p, {n, 0, 72}] (* Jayanta Basu, May 23 2013 *)

CROSSREFS

Cf. A056208.

Sequence in context: A307392 A046886 A257246 * A257245 A329245 A155047

Adjacent sequences:  A056203 A056204 A056205 * A056207 A056208 A056209

KEYWORD

nonn

AUTHOR

Labos Elemer, Oct 06 2000

EXTENSIONS

a(0) from Jayanta Basu, May 23 2013

STATUS

approved

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Last modified July 11 15:58 EDT 2020. Contains 335626 sequences. (Running on oeis4.)