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%I #10 Feb 27 2019 13:55:50
%S 0,1,2,3,6,7,8,10,16,17,35,53,121,155,178,487,880,1153,2136,2790,2803,
%T 5775,5845,5971,7131,13213,13813,17153,31461,38735,93577,188457
%N Numbers k such that (16*10^k + 161)/3 is prime.
%C For k>1, numbers n such that the digit 5 followed by k-2 occurrences of the digit 3 followed by the digits 87 is prime (see Example section).
%C a(33) > 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 53w87.</a>
%e 3 is in this sequence because (16*10^3 + 161)/3 = 5387 is prime.
%e Initial terms and primes associated:
%e a(1) = 0, 59;
%e a(2) = 1, 107;
%e a(3) = 2, 587;
%e a(4) = 3, 5387;
%e a(5) = 6, 5333387, etc.
%t Select[Range[0, 100000], PrimeQ[(16*10^# + 161)/3] &]
%o (PARI) is(n)=ispseudoprime((16*10^n + 161)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more
%O 1,3
%A _Robert Price_, May 18 2016
%E a(32) from _Robert Price_, Feb 27 2019
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