A102997 - OEIS

%I #25 Jan 17 2019 13:44:07

%S 1,463

%N Numbers n such that 4*10^n + 8*R_n - 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (44*10^n-71)/9 is prime.

%C No other terms below 10^5.

%C a(3) > 2*10^5. - _Robert Price_, Oct 15 2015

%C a(3) > 8*10^5, if it exists! - _Robert Price_, Dec 31 2016

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/48881.htm#prime">Prime numbers of the form 488...881</a>.

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

%F a(n) = A101734(n) + 1.

%t Do[ If[ PrimeQ[(44*10^n - 71)/9], Print[n]], {n, 10000}]

%o (PARI) for(n=0, 1000, if(isprime((44*10^n-71)/9), print1(n", "))) \\ _Altug Alkan_, Oct 15 2015

%Y Cf. A002275, A101734.

%K bref,more,nonn

%O 1,2

%A _Robert G. Wilson v_, Jan 17 2005