A271640 Numbers k such that 3*10^k + 73 is prime.

1, 2, 5, 6, 13, 37, 50, 55, 71, 89, 217, 352, 355, 398, 449, 668, 742, 870, 1360, 1579, 2848, 3774, 5039, 5051, 6134, 6824, 7255, 12586, 17106, 27502, 30581, 33817, 97399, 170800, 172219, 177872

Offset: 1

Author

Robert Price, Apr 11 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 0 followed by the digits 73 is prime (see Example section).

a(37) > 2*10^5.

Examples

			5 is in this sequence because 3*10^5 + 73 = 300073 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 373;
a(3) = 5, 300073;
a(4) = 6, 3000073;
a(5) = 13, 30000000000073, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 30w73.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[3*10^# + 73] &]

PARI

is(n)=ispseudoprime(3*10^n + 73) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(34)-a(36) from Robert Price, Aug 10 2018