A283236 Numbers k such that (86*10^k - 329)/9 is prime.

1, 2, 7, 22, 50, 76, 77, 130, 193, 259, 347, 590, 665, 838, 1516, 3512, 3566, 3688, 5393, 5408, 5875, 10160, 24238, 127967

Offset

1,2

Comments

For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 5 followed by the digits 19 is prime (see Example section).

a(25) > 2*10^5.

Links

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 95w19.

Example

2 is in this sequence because (86*10^2 - 329)/9 = 919 is prime.
Initial terms and associated primes:
a(1) = 1, 59;
a(2) = 2, 919;
a(3) = 7, 95555519;
a(4) = 22, 95555555555555555555519;
a(5) = 50, 955555555555555555555555555555555555555555555555519; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[(86*10^# - 329)/9] &]

Crossrefs

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

Sequence in context: A284921 A174236 A131856 * A007344 A153536 A153564

Adjacent sequences: A283233 A283234 A283235 * A283237 A283238 A283239

Keyword

nonn,more,hard

Author

Robert Price, Mar 03 2017

Extensions

a(24) from Robert Price, Jan 11 2020

Status

approved