A287687 Numbers k such that 9*10^k - 29 is prime.

1, 3, 5, 6, 15, 18, 21, 79, 291, 325, 359, 397, 455, 539, 735, 1164, 1653, 1795, 1829, 2622, 3798, 4013, 4795, 8823, 9349, 9366, 97247, 111201

Offset

1,2

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 9 followed by the digits 71 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 89w71.

Example

3 is in this sequence because 9*10^3 - 29 = 8971 is prime.
Initial terms and associated primes:
a(1) = 1, 61;
a(2) = 3, 8971;
a(3) = 5, 899971;
a(4) = 6, 8999971;
a(5) = 15, 8999999999999971; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[9*10^# - 29] &]

Crossrefs

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

Sequence in context: A030052 A227963 A099678 * A348658 A290761 A192119

Adjacent sequences: A287684 A287685 A287686 * A287688 A287689 A287690

Keyword

nonn,more,hard

Author

Robert Price, May 29 2017

Extensions

a(28) from Robert Price, Sep 25 2019

Status

approved