A103041 - OEIS

%I #16 Jan 17 2019 13:44:07

%S 2,5,8,17,20,65,83,90,108,252,335,1488,6356,65712,96798

%N Numbers n such that 6*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

%C Also numbers n such that (59*10^n+31)/9 is prime.

%C a(16) > 10^5. - _Robert Price_, Sep 13 2015

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/6/65559.htm#prime">Prime numbers of the form 655...559</a>.

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

%F a(n) = A101534(n) + 1.

%t Do[ If[ PrimeQ[(59*10^n + 31)/9], Print[n]], {n, 0, 10000}]

%o (PARI) is(n)=isprime(6*10^n + 5*(10^n-1)/9 + 4) \\ _Anders Hellström_, Sep 13 2015

%Y Cf. A002275, A101534.

%K more,nonn

%O 1,1

%A _Robert G. Wilson v_, Jan 18 2005

%E a(14)-a(15) from _Robert Price_, Sep 13 2015