A270613 Numbers k such that (68*10^k + 7)/3 is prime.

1, 2, 3, 4, 7, 10, 24, 25, 29, 34, 35, 37, 46, 49, 88, 103, 290, 381, 484, 696, 751, 886, 999, 1750, 5062, 6214, 9740, 12558, 16551, 24674, 28600, 37427, 48032, 61991, 70148, 72516, 99441, 179656

Offset: 1

Author

Robert Price, Mar 20 2016

Keywords

• nonn
• more

Comments

Numbers k such that the digits 22 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section).

a(39) > 3*10^5.

Examples

			3 is in this sequence because (68*10^3+7)/3 = 22669 is prime.
Initial terms and associated primes:
a(1) = 1, 229;
a(2) = 2, 2269;
a(3) = 3, 22669;
a(4) = 4, 226669;
a(5) = 7, 226666669, etc.
		

Links

• Makoto Kamada, Search for 226w9.

Crossrefs

Cf. A056654, A268448, A269303, A270339.

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(68*10^# + 7)/3] &]

PARI

lista(nn) = for(n=1, nn, if(ispseudoprime((68*10^n + 7)/3), print1(n, ", "))); \\ Altug Alkan, Mar 20 2016

Extensions

a(38) from Robert Price, Jan 16 2020