A272195 Numbers k such that (64*10^k + 287)/9 is prime.

1, 2, 4, 5, 7, 8, 13, 16, 22, 112, 134, 139, 250, 445, 475, 512, 544, 1318, 1588, 3307, 4216, 4457, 4474, 4979, 6241, 9551, 17939, 20405, 48106, 54467, 144797

Offset: 1

Author

Robert Price, Apr 22 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 1 followed by the digits 43 is prime (see Example section).

a(32) > 2*10^5.

Examples

			5 is in this sequence because (64*10^5 + 287)/9 = 711143 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 743;
a(3) = 4, 71143;
a(4) = 5, 711143;
a(5) = 7, 71111143, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 71w43.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(64*10^#n + 287)/9] &]

PARI

lista(nn) = for(n=1, nn, if(ispseudoprime((64*10^n + 287)/9), print1(n, ", "))); \\ Altug Alkan, Apr 22 2016

Extensions

a(31) from Robert Price, Apr 13 2019