A205236 Least prime p > 3 such that 2^n + p*2^k - 1 is prime for some k with n/3 < k < n+1

5, 5, 5, 7, 5, 5, 5, 7, 5, 5, 5, 11, 5, 5, 5, 7, 5, 5, 5, 7, 5, 5, 5, 11, 5, 5, 5, 7, 5, 5, 5, 7, 5, 5, 5, 11, 5, 5, 5, 7, 5, 5, 5, 7, 5, 5, 13, 11, 5, 5, 5, 7, 5, 5, 5, 7, 5, 5, 11, 17, 7, 5, 5, 7, 5, 5, 5, 7, 5, 5, 5, 11, 7, 5, 5, 7, 5, 5, 7, 7, 11, 5, 5

Offset

1,1

Comments

The prime p seems to be < 31.

Links

Pierre CAMI, Table of n, a(n) for n = 1..10800

Example

2^1+5*2^1-1=11 prime so p=5 for n=1.
2^2+5*2^2-1=23 prime so p=5 for n=2.
2^3+5*2^3-1=47 prime so p=5 for n=3.

Prog

PFGW64 from Primeform group and SCRIPTIFY
Command : pfgw64 -f in.txt
in.txt file :
SCRIPT
DIM nn, 0
DIM mm
DIM kk
DIMS tt
OPENFILEOUT myfile, prem.txt
LABEL loopn
SET nn, nn+1
IF nn>10800 THEN END
SET kk, 2
LABEL loopk
SET kk, kk+1
SET mm, nn/3
LABEL loopm
SET mm, mm+1
IF mm>nn THEN GOTO loopk
SETS tt, %d, %d, %d\ ; nn; p(kk); mm
PRP 2^nn+p(kk)*2^mm-1, tt
IF ISPRIME THEN GOTO a
IF ISPRP THEN GOTO a
GOTO loopm
LABEL a
WRITE myfile, tt
GOTO loopn

Crossrefs

Cf. A205237.

Sequence in context: A092279 A159002 A127934 * A266948 A176172 A204911

Adjacent sequences: A205233 A205234 A205235 * A205237 A205238 A205239

Keyword

nonn

Author

Pierre CAMI, Jan 24 2012

Status

approved