A282281 Numbers k such that (107*10^k - 17)/9 is prime.

2, 3, 8, 12, 24, 105, 140, 231, 234, 260, 294, 354, 602, 813, 1562, 2961, 3450, 5622, 8121, 9014, 23052, 38505, 41139, 63576

Offset

1,1

Comments

For k>0, numbers such that the digits 11 followed by k-1 occurrences of the digit 8 followed by the digit 7 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 118w7.

Example

3 is in this sequence because (107*10^3 - 17)/9 = 11887 is prime.
Initial terms and primes associated:
a(1) = 2, 1187;
a(2) = 3, 11887;
a(3) = 8, 1188888887;
a(4) = 12, 11888888888887;
a(5) = 24, 11888888888888888888888887; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(107*10^# - 17)/9] &]

Crossrefs

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

Sequence in context: A218542 A194452 A242516 * A321175 A079980 A025080

Adjacent sequences: A282278 A282279 A282280 * A282282 A282283 A282284

Keyword

nonn,more,hard

Author

Robert Price, Feb 10 2017

Status

approved