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%I #13 Jan 17 2019 13:44:09
%S 0,2,3,6,12,15,17,24,26,30,156,341,519,1284,1455,1841,1874,3410,3890,
%T 6185,8472,8696,67784,72174,84779,87669,99693,114296,119474,152253,
%U 183659
%N Numbers k such that (4*10^k + 149)/9 is prime.
%C For k>1, numbers such that k-2 occurrences of the digit 4 followed by the digits 61 is prime (see Example section).
%C a(32) > 2*10^5.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/primedifficulty.txt">Search for 4w61.</a>
%e 3 is in this sequence because (4*10^3 + 149)/9 = 461 is prime.
%e Initial terms and primes associated:
%e a(1) = 0, 17;
%e a(2) = 2, 61;
%e a(3) = 3, 461;
%e a(4) = 6, 444461;
%e a(5) = 12, 444444444461; etc.
%t Select[Range[0, 100000], PrimeQ[(4*10^# + 149)/9] &]
%o (PARI) isok(k) = ispseudoprime((4*10^k + 149)/9); \\ _Altug Alkan_, Apr 12 2018
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Mar 30 2017
%E a(28)-a(31) from _Robert Price_, Apr 12 2018
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