A275525 Numbers k such that (73*10^k + 107)/9 is prime.

2, 3, 5, 6, 11, 12, 26, 32, 36, 75, 137, 143, 279, 290, 363, 716, 770, 1377, 1638, 4470, 5952, 10526, 15132, 27054, 81485

Offset: 1

Author

Robert Price, Aug 11 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 1 followed by the digits 23 is prime (see Example section).

a(26) > 10^5.

Examples

			3 is in this sequence because (73*10^3+107)/9 = 8123 is prime.
Initial terms and associated primes:
a(1) = 2, 823;
a(2) = 3, 8123;
a(3) = 5, 811123;
a(4) = 6, 8111123;
a(5) = 11, 811111111123, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 81w23.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(73*10^#+107)/9] &]

PARI

lista(nn) = for(n=1, nn, if(ispseudoprime((73*10^n+107)/9), print1(n, ", "))); \\ Altug Alkan, Aug 11 2016