A213884 For the smallest k >= 1, the smallest single-digit j such that (10^k-j)*10^n-1 is prime.

1, 4, 1, 2, 2, 5, 1, 2, 1, 2, 1, 4, 4, 5, 5, 1, 4, 7, 1, 4, 2, 4, 4, 1, 2, 8, 7, 4, 1, 1, 2, 1, 1, 4, 7, 4, 1, 1, 7, 4, 8, 2, 7, 4, 8, 8, 7, 2, 2, 1, 8, 2, 8, 5, 7, 1, 8, 4, 8, 1, 4, 1, 4, 7, 1, 2, 8, 2, 4, 1, 4, 8, 4, 5, 8, 2, 1, 2, 7, 7, 5, 1, 4, 8, 7, 4, 1, 4, 2, 2, 4, 5

Offset

1,2

Comments

These j are the associated shifts to be paired with the k-values of A213883. There are no multiples of 3 here, as explained in A213883.

For the first 2200 values of n, there is always at least one pair (k,j) that delivers a prime with the conditions.

Links

Pierre CAMI, Table of n, a(n) for n = 1..2200

Example

j=1 associated with the prime 89, j=4 associated with 599, j=1 associated with 8999, j=2 with 79999 are the first 4 entries.

Maple

A213884 := proc(n)
    for k from 1 do
        for j from 0 to 9 do
            if isprime( (10^k-j)*10^n-1) then
                return j;
            end if;
        end do:
    end do:
    return 0 ;
end proc: # R. J. Mathar, Jul 20 2012

Prog

SCRIPT
DIM nn, 0
DIM jj
DIM kk
DIMS tt
OPENFILEOUT myfile, a(n).txt
LABEL loopn
SET nn, nn+1
IF nn>2200 THEN END
SET kk, 0
LABEL loopk
SET kk, kk+1
IF kk>2*nn THEN GOTO loopn
SET jj, 0
LABEL loopj
SET jj, jj+1
IF jj%3==0 THEN SET jj, jj+1
IF jj>9 THEN GOTO loopk
SETS tt, %d, %d, %d\,; nn; kk; jj
PRP (10^kk-jj)*10^nn-1, tt
IF ISPRP THEN GOTO a
IF ISPRIME THEN GOTO a
GOTO loopj
LABEL a
WRITE myfile, tt
GOTO loopn

Crossrefs

Cf. A213883.

Sequence in context: A279605 A054713 A371853 * A117021 A222213 A010473

Adjacent sequences: A213881 A213882 A213883 * A213885 A213886 A213887

Keyword

nonn

Author

Pierre CAMI, Jun 29 2012

Status

approved