A259141 Numbers k such that R_k + 9*10^k + 8 is prime, where R_k = 11...11 is the repunit (A002275) of length k.

0, 2, 246, 1140, 10394, 43880

Offset

1,2

Comments

Also, numbers k such that (82*10^k + 71)/9 is prime.

Terms from Kamada data.

Note Kamada does not recognize k=0 as 17 is a degenerate case of form ABB..BBA.

a(7) > 10^5.

Links

Table of n, a(n) for n=1..6.

Makoto Kamada, Near-repdigit numbers of the form ABB...BBA.

Makoto Kamada, Prime numbers of the form 911...119.

Index entries for primes involving repunits.

Example

For k=2, R_2 + 9*10^k + 8 = 11 + 900 + 8 = 919 which is prime.

Mathematica

Select[Range[0, 100000], PrimeQ[(82*10^#+71)/9] &]

Crossrefs

Cf. A002275.

Sequence in context: A049333 A140162 A145712 * A065664 A244926 A024031

Adjacent sequences: A259138 A259139 A259140 * A259142 A259143 A259144

Keyword

more,hard,nonn

Author

Robert Price, Jun 18 2015

Status

approved