Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #26 Jul 24 2021 02:25:27
%S 11,17,197,317,347,431,977,1949,1991,2913,6317,9725,36599
%N Positive numbers k such that (10^(k+3)*3277 + 3167)/9 is prime.
%C Or '364'||...'1'...||'463' in decimal form is prime ('1' concatenated k times to which the prefix '364' and the suffix '463' are concatenated once).
%C a(1)..a(8) themselves are primes.
%e 11 is a term as 36411111111111463 is prime (as a string, it consists of '1' concatenated 11 times to which the prefix '364' and the suffix '463' are concatenated once).
%t ParallelMap[ If[ PrimeQ[(10^(#+3)*3277+3167)/9], #, Nothing]&, Range[3000]]
%o (PARI) is(n)=ispseudoprime((10^(n+3)*3277+3167)/9) \\ _Charles R Greathouse IV_, Jun 13 2017
%K nonn,hard,more,base
%O 1,1
%A _Mikk Heidemaa_, May 17 2017
%E a(13) from _Giovanni Resta_, May 25 2017