A274976 Numbers k such that (26*10^k + 31)/3 is prime.

0, 1, 2, 3, 4, 7, 9, 57, 98, 122, 123, 249, 304, 318, 339, 374, 390, 476, 619, 1358, 1724, 3351, 5046, 5572, 6685, 9421, 14362, 97353

Offset: 1

Author

Robert Price, Jul 14 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 77 is prime (see Example section).

a(29) > 10^5.

Examples

			3 is in this sequence because (26*10^3 + 31)/3 = 877 is prime.
Initial terms and associated primes:
a(1) = 0, 19;
a(2) = 1, 97;
a(3) = 2, 877;
a(4) = 3, 8677;
a(5) = 4, 86677, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 86w77.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(26*10^# + 31)/3] &]

PARI

is(n)=ispseudoprime((26*10^n+31)/3) \\ Charles R Greathouse IV, Jun 13 2017