A282508 Numbers k such that (52*10^k - 1)/3 is prime.

0, 1, 2, 3, 8, 9, 19, 20, 24, 28, 70, 102, 123, 344, 2228, 3282, 4554, 5370, 5830, 12328, 21742, 27937, 49261, 89037

Offset

1,3

Comments

For k > 1, numbers k such that the digits 17 followed by k occurrences of the digit 3 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 173w.

Example

3 is in this sequence because (52*10^3 - 1)/3 = 17333 is prime.
Initial terms and associated primes:
a(1) = 0, 17;
a(2) = 1, 173;
a(3) = 2, 1733;
a(4) = 3, 17333;
a(5) = 8, 1733333333; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(52*10^# - 1)/3] &]

Crossrefs

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

Sequence in context: A309017 A376191 A247375 * A103026 A098506 A279090

Adjacent sequences: A282505 A282506 A282507 * A282509 A282510 A282511

Keyword

nonn,more,hard

Author

Robert Price, Feb 16 2017

Status

approved