A276672 Numbers k such that (19*10^k + 101) / 3 is prime.

1, 3, 4, 9, 10, 12, 13, 16, 20, 37, 57, 66, 106, 116, 127, 355, 396, 547, 2289, 3777, 4500, 7821, 15663, 22746, 25978, 30434, 39682, 119716, 133390, 145093, 200260

Offset: 1

Author

Robert Price, Sep 12 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 3 followed by the digits 67 is prime (see Example section).

a(32) > 3*10^5. - Robert Price, Jul 13 2023

Examples

			3 is in this sequence because (19*10^3 + 101) / 3 = 6367 is prime.
Initial terms and associated primes:
a(1) = 1, 97;
a(2) = 3, 6367;
a(3) = 4, 63367;
a(4) = 9, 6333333367;
a(5) = 10, 63333333367, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 63w67.

Crossrefs

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

Programs

Magma

[n: n in [0..400] |IsPrime((19*10^n + 101) div 3)]; // Vincenzo Librandi, Sep 13 2016

Mathematica

Select[Range[0, 100000], PrimeQ[(19*10^# + 101) / 3] &]

PARI

is(n)=ispseudoprime((19*10^n + 101)/3) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(28)-a(30) from Robert Price, Sep 01 2019

a(31) from Robert Price, Jul 13 2023