A283185 Numbers k such that (86*10^k + 121)/9 is prime.

0, 1, 4, 6, 24, 52, 60, 76, 94, 106, 136, 196, 283, 319, 486, 1560, 1615, 1747, 2188, 2359, 5004, 5608, 9301, 22086, 30391, 76128, 90588, 139315

Offset

1,3

Comments

For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 5 followed by the digits 69 is prime (see Example section).

a(29) > 2*10^5.

Links

Table of n, a(n) for n=1..28.

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

Makoto Kamada, Search for 95w69.

Example

4 is in this sequence because (86*10^4 + 121)/9 = 95569 is prime.
Initial terms and associated primes:
a(1) = 0, 23;
a(2) = 1, 109;
a(3) = 4, 95569;
a(4) = 6, 9555569;
a(5) = 24, 9555555555555555555555569; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(86*10^# + 121)/9] &]

Crossrefs

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

Sequence in context: A098660 A363631 A122174 * A034458 A240290 A067001

Adjacent sequences: A283182 A283183 A283184 * A283186 A283187 A283188

Keyword

nonn,more,hard

Author

Robert Price, Mar 02 2017

Extensions

a(28) from Robert Price, Aug 30 2019

Status

approved