login
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
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.
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
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Jun 18 2015
STATUS
approved