

A206553


Least prime p > 3 such that 2^n + p*2^floor((n+1)/2)  1 is prime.


2



5, 5, 13, 7, 5, 5, 7, 7, 11, 13, 13, 11, 5, 11, 37, 11, 5, 23, 13, 47, 89, 13, 19, 19, 11, 7, 19, 23, 17, 13, 19, 43, 29, 79, 61, 17, 191, 43, 337, 53, 29, 17, 13, 13, 29, 11, 19, 11, 11, 13, 43, 163, 29, 13, 7, 53, 23, 97, 31, 29, 41, 83, 79, 23, 191, 97
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OFFSET

1,1


LINKS

Pierre CAMI, Table of n, a(n) for n = 1..10000


EXAMPLE

2^1+5*2^11 = 11 prime so a(1) = 5.
2^2+5*2^11 = 13 prime so a(2) = 5.


PROG

PFGW64 from Primeform group and SRYPTIFY
command : pfgw64 f in.txt
in.txt file :
SCRIPT
DIM kk
DIM nn, 0
DIM mm
DIMS tt
OPENFILEOUT myfil, prem.txt
LABEL loopn
SET nn, nn+1
IF nn>10000 THEN END
IF nn%2==0 THEN SET mm, nn/2
IF nn%2==1 THEN SET mm, nn/2+1
SET kk, 2
LABEL loopk
SET kk, kk+1
SETS tt, %d, %d, %d, %d\ ; nn; kk; p(kk); mm
PRP (2^(nnmm)+p(kk))*2^mm1, tt
IF ISPRP THEN GOTO a
IF ISPRIME THEN GOTO a
GOTO loopk
LABEL a
WRITE myfil, tt
GOTO loopn
(Haskell)
a206553 n = head [p  p < drop 2 a000040_list,
a010051 (2^n + p*2^(div (n+1) 2)  1) == 1]
 Reinhard Zumkeller, Feb 10 2012


CROSSREFS

Cf. A206554.
Cf. A010051, A000040.
Sequence in context: A338085 A302676 A339947 * A122213 A224067 A049735
Adjacent sequences: A206550 A206551 A206552 * A206554 A206555 A206556


KEYWORD

nonn


AUTHOR

Pierre CAMI, Feb 09 2012


STATUS

approved



