A274037 Numbers k such that 3*10^k - 49 is prime.

2, 5, 6, 10, 16, 29, 35, 82, 107, 170, 185, 204, 223, 226, 388, 512, 1586, 2137, 3182, 7325, 7346, 8143, 8746, 11322, 11497, 13279, 44681, 108624, 183872

Offset: 1

Author

Robert Price, Jun 07 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section).

a(31) > 2*10^5.

Examples

			5 is in this sequence because 3*10^5-49 = 299951 is prime.
Initial terms and associated primes:
a(1) = 2, 251;
a(2) = 5, 299951;
a(3) = 6, 2999951;
a(4) = 10, 29999999951;
a(5) = 16, 29999999999999951, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 29w51.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[3*10^# - 49] &]

PARI

is(n)=ispseudoprime(3*10^n - 49) \\ Charles R Greathouse IV, Jun 08 2016

Extensions

a(28)-a(29) from Robert Price, Jul 29 2018