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%I #12 Jan 17 2019 13:44:08
%S 2,3,4,9,10,13,15,24,26,38,39,42,433,489,495,513,597,829,2019,2738,
%T 3096,3691,5437,7537,8536,34125,40105,41790,52713,104811,173809,175860
%N Numbers k such that 2*10^k - 87 is prime.
%C For k>1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 9 followed by the digits 13 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 19w13.</a>
%e 3 is in this sequence because 2*10^3 - 87 = 1913 is prime.
%e Initial terms and primes associated:
%e a(1) = 2, 113;
%e a(2) = 3, 1913;
%e a(3) = 4, 19913;
%e a(4) = 9, 1999999913;
%e a(5) = 10, 19999999913, etc.
%t Select[Range[0, 100000], PrimeQ[2*10^# - 87] &]
%o (PARI) is(n)=ispseudoprime(2*10^n - 87) \\ _Charles R Greathouse IV_, Jun 08 2016
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more
%O 1,1
%A _Robert Price_, Jun 03 2016
%E a(30)-a(32) from _Robert Price_, Apr 13 2018
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