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

%I A271618 #21 Jun 09 2024 16:13:05
%S A271618 3,4,6,14,15,16,20,46,52,114,165,468,504,568,713,748,899,958,992,1043,
%T A271618 1348,2388,3182,4102,8847,10899,11908,18852,25214,40151,40290,51207,
%U A271618 71910,166324
%N A271618 Numbers k such that 10^k - 801 is prime.
%C A271618 For k > 2, numbers k such that k-3 occurrences of the digit 9 followed by the digits 199 is prime (see Example section).
%C A271618 a(35) > 2*10^5.
%H A271618 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H A271618 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 9w199</a>.
%e A271618 6 is in this sequence because 10^6-801 = 999199 is prime.
%e A271618 Initial terms and associated primes:
%e A271618 a(1) = 3, 199;
%e A271618 a(2) = 4, 9199;
%e A271618 a(3) = 6, 999199;
%e A271618 a(4) = 14, 99999999999199;
%e A271618 a(5) = 15, 999999999999199, etc.
%t A271618 Select[Range[0, 100000], PrimeQ[10^#-801] &]
%o A271618 (PARI) is(n)=ispseudoprime(10^n-801) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A271618 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K A271618 nonn,more
%O A271618 1,1
%A A271618 _Robert Price_, Apr 11 2016
%E A271618 a(34) from _Robert Price_, Feb 14 2018