A283246 Numbers k such that (17*10^k - 179)/9 is prime.

4, 5, 10, 13, 16, 106, 130, 148, 880, 1261, 2560, 2629, 3730, 5284, 7411, 8255, 9091, 9490, 10171, 14033, 25618, 39382, 47452

Offset

1,1

Comments

For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 8 followed by the digits 69 is prime (see Example section).

a(24) > 2*10^5.

Links

Table of n, a(n) for n=1..23.

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

Makoto Kamada, Search for 18w69.

Example

5 is in this sequence because (17*10^5 - 179)/9 = 188869 is prime.
Initial terms and associated primes:
a(1) = 4, 18869;
a(2) = 5, 188869;
a(3) = 10, 18888888869;
a(4) = 13, 18888888888869;
a(5) = 16, 18888888888888869; etc.

Mathematica

Select[Range[2, 100000], PrimeQ[(17*10^# - 179)/9] &]

Prog

(PARI) is(n)=isprime((17*10^k - 179)/9) \\ Charles R Greathouse IV, Mar 05 2017

Crossrefs

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

Sequence in context: A222353 A094415 A114517 * A236283 A378273 A357865

Adjacent sequences: A283243 A283244 A283245 * A283247 A283248 A283249

Keyword

nonn,more,hard

Author

Robert Price, Mar 05 2017

Status

approved