A274331 Numbers k such that (148*10^k - 1)/3 is prime.

2, 3, 4, 5, 9, 27, 35, 44, 88, 104, 205, 290, 302, 381, 400, 686, 917, 1150, 2278, 2757, 3220, 3316, 7469, 9535, 21442, 46409, 103718, 123688, 147139

Offset: 1

Author

Robert Price, Jun 18 2016

Keywords

• nonn
• more

Comments

Numbers k such that the digits 49 followed by k occurrences of the digit 3 is prime (see Example section).

a(30) > 2*10^5.

Examples

			3 is in this sequence because (148*10^3-1)/3 = 233329 is prime.
Initial terms and associated primes:
a(1) = 2, 4933;
a(2) = 3, 49333;
a(3) = 4, 493333;
a(4) = 5, 4933333;
a(5) = 9, 49333333333, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 493w.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(148*10^# - 1)/3] &]

PARI

is(n)=ispseudoprime((148*10^n - 1)/3) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(27)-a(29) from Robert Price, Mar 18 2020