A276046 Numbers k such that (26*10^k - 23)/3 is prime.

1, 2, 10, 16, 78, 97, 125, 138, 192, 242, 290, 373, 408, 467, 583, 892, 899, 1709, 1944, 2154, 3618, 5225, 8974, 9377, 12504, 20042, 49106, 63073, 92152, 147973

Offset: 1

Author

Robert Price, Aug 17 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 59 is prime (see Example section).

a(31) > 2*10^5.

Examples

			2 is in this sequence because (26*10^2 - 23)/3 = 859 is prime.
Initial terms and associated primes:
a(1) = 1, 79;
a(2) = 2, 859;
a(3) = 10, 86666666659;
a(4) = 16, 86666666666666659, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 86w59.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(26*10^# - 23)/3] &]

PARI

is(n)=ispseudoprime((26*10^n - 23)/3) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(30) from Robert Price, Dec 19 2019