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%I #15 Sep 08 2022 08:46:12
%S 10,12,63,69,156,328,340,344,444,672,894,1464,1670,1708,2010,4306,
%T 7888,8864,9478,9621,26004,36992,71600,98738,118949,130565,140326,
%U 183452,211983,225618
%N Numbers k such that 9*R_(k+2) - 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C Also, numbers k such that 96*10^k - 1 is prime.
%C Terms from Kamada.
%C 846519 reported to Kamada by Bruno DallOsto is also in this sequence. It may or may not be a(31).
%C a(31) > 230000.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/abaaa.htm">Near-repdigit numbers of the form ABAA...AA</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/95999.htm#prime">Prime numbers of the form 9599...99</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%e For k=10, 9*R_12 - 4*10^10 = 999999999999 - 40000000000 = 959999999999 which is prime.
%t Select[Range[0, 230000], PrimeQ[96*10^#-1 ] &]
%o (Magma) [n: n in [0..400] | IsPrime(96*10^n-1)]; // _Vincenzo Librandi_, Apr 15 2015
%Y Cf. A002275.
%K more,hard,nonn
%O 1,1
%A _Robert Price_, Apr 14 2015
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