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%I #20 Aug 21 2019 02:46:13
%S 1,2,3,8,24,49,57,74,104,131,144,162,182,246,302,352,557,581,589,704,
%T 939,1181,1937,2157,4463,6013,7266,8504,8691,16129,20108,40677,74234,
%U 112018
%N Numbers k such that 8*10^k - 49 is prime.
%C For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section).
%C a(35) > 2*10^5.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/primedifficulty.txt">Search for 79w51</a>.
%e 3 is in this sequence because 8*10^3 - 49 = 7951 is prime.
%e Initial terms and primes associated:
%e a(1) = 1, 31;
%e a(2) = 2, 751;
%e a(3) = 3, 7951;
%e a(4) = 8, 799999951;
%e a(6) = 24, 7999999999999999999999951, etc.
%t Select[Range[0, 100000], PrimeQ[8*10^# - 49] &]
%o (PARI) is(n)=isprime(8*10^n - 49) \\ _Charles R Greathouse IV_, Feb 16 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929.
%K nonn,more
%O 1,2
%A _Robert Price_, Apr 03 2016
%E a(34) from _Robert Price_, Aug 20 2019
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