A266582 Numbers k such that (265*10^k - 7)/3 is prime.

1, 2, 4, 9, 13, 14, 16, 46, 99, 112, 116, 127, 146, 208, 512, 848, 1132, 2167, 2482, 2666, 3625, 14410, 16567, 21529, 26272, 69554, 69602

Offset: 1

Author

Robert Price, Jul 10 2016

Keywords

• nonn
• more

Comments

For k > 0, numbers k such that the digits 88 followed by k-1 occurrences of the digit 3 followed by the digit 1 is prime (see Example section).

a(28) > 10^5.

Examples

			4 is in this sequence because (265*10^4 - 7)/3 = 883331 is prime.
Initial terms and associated primes:
a(1) = 1, 881;
a(2) = 2, 8831;
a(3) = 4, 883331l
a(4) = 9, 88333333331;
a(5) = 13, 883333333333331, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 883w1.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(265*10^# - 7)/3] &]

PARI

is(n)=ispseudoprime((265*10^n-7)/3) \\ Charles R Greathouse IV, Jun 13 2017