A293910 Numbers k such that (26*10^k - 173)/3 is prime.

1, 2, 3, 8, 11, 13, 17, 28, 46, 67, 136, 536, 619, 746, 2420, 2672, 8228, 10861, 13424, 16047, 18075, 37720, 56371, 75055

Offset

1,2

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 09 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 86w09.

Example

2 is in this sequence because (26*10^2 - 173)/3 = 809 is prime.
Initial terms and associated primes:
a(1) = 1, 29;
a(2) = 2, 809;
a(3) = 3, 8609;
a(4) = 8, 866666609;
a(5) = 11, 866666666609; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[(26*10^# - 173)/3] &]

Crossrefs

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

Sequence in context: A201541 A084917 A134713 * A173269 A364217 A050557

Adjacent sequences: A293907 A293908 A293909 * A293911 A293912 A293913

Keyword

nonn,more,hard

Author

Robert Price, Oct 19 2017

Status

approved