A271618 Numbers k such that 10^k - 801 is prime.

3, 4, 6, 14, 15, 16, 20, 46, 52, 114, 165, 468, 504, 568, 713, 748, 899, 958, 992, 1043, 1348, 2388, 3182, 4102, 8847, 10899, 11908, 18852, 25214, 40151, 40290, 51207, 71910, 166324

Offset: 1

Author

Robert Price, Apr 11 2016

Keywords

• nonn
• more

Comments

For k > 2, numbers k such that k-3 occurrences of the digit 9 followed by the digits 199 is prime (see Example section).

a(35) > 2*10^5.

Examples

			6 is in this sequence because 10^6-801 = 999199 is prime.
Initial terms and associated primes:
a(1) = 3, 199;
a(2) = 4, 9199;
a(3) = 6, 999199;
a(4) = 14, 99999999999199;
a(5) = 15, 999999999999199, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 9w199.

Crossrefs

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

Programs

Mathematica

Select[Range[0, 100000], PrimeQ[10^#-801] &]

PARI

is(n)=ispseudoprime(10^n-801) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(34) from Robert Price, Feb 14 2018