A271147 Numbers k such that (28*10^k + 113)/3 is prime.

0, 1, 2, 3, 4, 6, 9, 12, 16, 22, 23, 42, 52, 57, 63, 117, 119, 208, 266, 324, 481, 779, 1244, 1289, 2998, 5522, 5599, 5771, 6820, 12367, 14737, 22612, 30623, 31596, 58956, 59133, 138240, 163709, 250655, 259897

Offset: 1

Author

Robert Price, Mar 31 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 71 is prime (see Example section).

a(41) > 3*10^5.

Examples

			3 is in this sequence because (28*10^3+113)/3 = 9371 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 1, 131;
a(3) = 2, 971;
a(4) = 3, 9371;
a(5) = 4, 93371;
a(6) = 6, 9333371, etc.
		

Links

• Makoto Kamada, Search for 93w71.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(28*10^# + 113)/3] &]

PARI

is(n)=ispseudoprime((28*10^n + 113)/3) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(37)-a(38) from Robert Price, Mar 13 2020

a(39)-a(40) from Robert Price, Jun 17 2023