A294913 Numbers k such that (89*10^k - 539)/9 is prime.

2, 3, 5, 8, 9, 18, 20, 26, 111, 141, 162, 236, 312, 383, 2093, 3926, 3981, 4935, 17126, 32070, 64608, 86802

Offset

1,1

Comments

For k > 1, numbers such that the digit 9 followed by k-2 occurrences of the digit 8 followed by the digits 29 is prime (see Example section).

a(23) > 2*10^5.

Links

Table of n, a(n) for n=1..22.

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

Makoto Kamada, Search for 98w29.

Example

2 is in this sequence because (89*10^2 - 539)/9 = 929 is prime.
Initial terms and primes associated:
a(1) = 2, 929;
a(2) = 3, 9829;
a(3) = 5, 988829;
a(4) = 8, 988888829;
a(5) = 9, 9888888829; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[(89*10^# - 539)/9] &]

Crossrefs

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

Sequence in context: A278334 A120057 A099422 * A056903 A229139 A293277

Adjacent sequences: A294910 A294911 A294912 * A294914 A294915 A294916

Keyword

nonn,more,hard

Author

Robert Price, Nov 10 2017

Status

approved