A271377 Numbers k such that (28*10^k - 43)/3 is prime.

1, 2, 3, 4, 5, 6, 7, 13, 43, 112, 114, 127, 242, 247, 251, 335, 450, 616, 816, 1237, 1448, 4303, 4865, 5414, 6427, 9045, 10391, 12651, 25071, 27901, 50362, 58843, 67378, 68107, 262655

Offset: 1

Author

Robert Price, Apr 05 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 19 is prime (see Example section).

a(36) > 3*10^5.

Examples

			3 is in this sequence because (28*10^3 - 43)/3 = 9319 is prime.
Initial terms and associated primes:
a(1) = 1, 79;
a(2) = 2, 919;
a(3) = 3, 9319;
a(4) = 4, 93319;
a(5) = 5, 933319, etc.
		

Links

• Makoto Kamada, Search for 93w19.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(28*10^# - 43)/3] &]

PARI

lista(nn) = for(n=1, nn, if(ispseudoprime((28*10^n - 43)/3), print1(n, ", "))); \\ Altug Alkan, Apr 05 2016

Extensions

a(35) from Robert Price, Jul 02 2023