A282809 Numbers k such that (82*10^k + 449)/9 is prime.

0, 3, 5, 6, 18, 21, 27, 36, 84, 95, 179, 492, 776, 1260, 4304, 5010, 5196, 7718, 15315, 20838, 20940, 24303, 26789, 72612, 157319

Offset

1,2

Comments

For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 1 followed by the digits 61 is prime (see Example section).

a(26) > 2*10^5.

Links

Table of n, a(n) for n=1..25.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 91w61.

Example

5 is in this sequence because (82*10^5 + 449)/9 = 911161 is prime.
Initial terms and associated primes:
a(1) = 0, 59;
a(2) = 3, 9161;
a(3) = 5, 911161;
a(4) = 6, 9111161;
a(5) = 18, 9111111111111111161; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(82*10^# + 449)/9] &] (* Corrected by Georg Fischer, Jul 22 2019 *)

Crossrefs

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A290761 A192119 A050563 * A168156 A295403 A272440

Adjacent sequences: A282806 A282807 A282808 * A282810 A282811 A282812

Keyword

nonn,more,hard

Author

Robert Price, Feb 22 2017

Extensions

a(25) from Robert Price, Nov 09 2019

Status

approved