A103101 - OEIS

%I #22 Jan 17 2019 13:44:07

%S 0,2,20,104,329,1442,1721,24887

%N Numbers n such that 9*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (86*10^n-23)/9 is prime.

%C a(9) > 10^5. - _Robert Price_, Nov 08 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/95553.htm#prime">Prime numbers of the form 955...553</a>.

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

%F a(n) = A101010(n-1) + 1, for n>1.

%t Do[ If[ PrimeQ[(86*10^n - 23)/9], Print[n]], {n, 0, 10000}]

%o (PARI) for(n=0, 1e5, if(isprime((86*10^n-23)/9), print1(n, ", "))); \\ _Altug Alkan_, Nov 08 2015

%Y Cf. A002275, A101010.

%K more,nonn

%O 1,2

%A _Robert G. Wilson v_, Jan 19 2005

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

%E Inserted a(1)=0 by _Robert Price_, Nov 08 2015