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A103098 Numbers n such that 9*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1

%I #17 Jan 17 2019 13:44:07

%S 30,41,228,581,1290,2580,3696,11390,21558

%N Numbers n such that 9*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (85*10^n-13)/9 is prime.

%C a(10) > 10^5. - _Robert Price_, Nov 05 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/94443.htm#prime">Prime numbers of the form 944...443</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%F a(n) = A101007(n) + 1.

%t Do[ If[ PrimeQ[(85*10^n - 13)/9], Print[n]], {n, 0, 10000}]

%Y Cf. A002275, A101007.

%K more,nonn

%O 1,1

%A _Robert G. Wilson v_, Jan 19 2005

%E a(8)-a(9) from Kamada data by _Robert Price_, Dec 14 2010

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Last modified March 28 15:28 EDT 2024. Contains 371254 sequences. (Running on oeis4.)