A273265 Numbers k such that (16*10^k + 161)/3 is prime.

0, 1, 2, 3, 6, 7, 8, 10, 16, 17, 35, 53, 121, 155, 178, 487, 880, 1153, 2136, 2790, 2803, 5775, 5845, 5971, 7131, 13213, 13813, 17153, 31461, 38735, 93577, 188457

Offset: 1

Author

Robert Price, May 18 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 3 followed by the digits 87 is prime (see Example section).

a(33) > 2*10^5.

Examples

			3 is in this sequence because (16*10^3 + 161)/3 = 5387 is prime.
Initial terms and associated primes:
a(1) = 0, 59;
a(2) = 1, 107;
a(3) = 2, 587;
a(4) = 3, 5387;
a(5) = 6, 5333387, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 53w87.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(16*10^# + 161)/3] &]

PARI

is(n)=ispseudoprime((16*10^n + 161)/3) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(32) from Robert Price, Feb 27 2019