A213881 k such that 10^(2*k+1)-j*10^k-1 is prime for some j = 1, 2, 4, 5, 7 or 8.

1, 5, 8, 9, 13, 14, 22, 26, 36, 43, 88, 104, 112, 118, 169, 181, 198, 352, 378, 530, 622, 697, 1136, 1246, 1315, 1579, 1798, 1918, 2874, 2917, 4228, 5876, 6768, 10052, 17864, 18077, 22652, 23034, 25448, 47509, 52140, 55862, 62938, 67404, 134739, 145126

Offset

1,2

Comments

The j values are either 7 and 8 for k=1. For larger k, there is one j only: 8, 7, 7, 8, 5, 5, 1, 5, 8, 4, 5, 4, 2, 8, 8, 4, 7, 1, 7, 4, 7, 5, 1, 7, 8, 1, 7, 7, 1, 4, 7, 7, 4, 5, 8, 8, 1, 5, 1, 1, 4, 7, 1, 7, 2.

The next k is probably near 160000 to 200000

Links

Table of n, a(n) for n=1..46.

Chris Caldwell, Palindrome

Chris Caldwell, Daren Bedwell

Example

10^3-7*10^1-1=929 prime as 10^3-8*10^1-1=919 so a(1)=1.

Prog

PFGW64 and SCRIPTIFY from Primeform Group
Command : pfgw64 -f in.txt
in.txt file :
SCRIPT
DIM nn, 0
DIM kk
DIMS tt
OPENFILEOUT myfile, a(n).txt
LABEL loopn
SET nn, nn+1
IF nn>200000 THEN END
SET kk, 0
LABEL loopk
SET kk, kk+1
IF kk%3==0 THEN SET kk, kk+1
IF kk>8 THEN GOTO loopn
SETS tt, %d, %d\,; nn; kk
PRP (10^(nn+1)-kk)*10^nn-1, tt
IF ISPRIME THEN GOTO a
IF ISPRP THEN GOTO a
GOTO loopk
LABEL a
WRITE myfile, tt
GOTO loopk
Results in a(n)

Crossrefs

Cf. A115073, A183187

Sequence in context: A314575 A286454 A293913 * A179832 A334919 A047616

Adjacent sequences: A213878 A213879 A213880 * A213882 A213883 A213884

Keyword

nonn,base

Author

Pierre CAMI, Jun 23 2012

Status

approved