A262937 Numbers k such that (28*10^k - 13) / 3 is prime.

0, 1, 2, 4, 5, 8, 10, 14, 17, 20, 33, 64, 80, 152, 158, 166, 194, 196, 198, 901, 971, 1289, 1595, 2921, 14390, 28781, 35840

Offset: 1

Author

Robert Price, Sep 23 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 29 is prime (see Example section).

a(28) > 3*10^5.

Examples

			2 is in this sequence because (28*10^2 - 13) / 3 = 929 is prime.
Initial terms and associated primes:
a(1) = 0, 5;
a(2) = 1, 89;
a(3) = 2, 929;
a(4) = 4, 93329;
a(5) = 5, 933329, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 93w29.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[(28*10^# - 13) / 3] &]

PARI

is(n)=ispseudoprime((28*10^n - 13)/3) \\ Charles R Greathouse IV, Jun 13 2017