A275323 Numbers k such that (19*10^k + 161)/9 is prime.

2, 3, 5, 6, 8, 18, 36, 59, 80, 162, 197, 200, 405, 432, 930, 1065, 1496, 1716, 3213, 5712, 6303, 7466, 14150, 23685, 54608, 59766

Offset: 1

Author

Robert Price, Jul 23 2016

Keywords

• nonn
• more

Comments

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

a(27) > 10^5.

Examples

			5 is in this sequence because (19*10^5 + 161)/9 = 211129 is prime.
Initial terms and associated primes:
a(1) = 2, 229;
a(2) = 3, 2129;
a(3) = 5, 211129;
a(4) = 6, 2111129;
a(5) = 8, 211111129, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 21w29.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(19*10^# + 161)/9] &]

PARI

is(n)=ispseudoprime((19*10^n+161)/9) \\ Charles R Greathouse IV, Jun 13 2017