%I #5 Dec 15 2017 17:36:57
%N Numbers n such that n*10^n + n - 1 is prime.
%C Not proved, only Fermat and Lucas PRPs. Next term is greater than 12000. Concerning primes of the form n * 10^n + n + 1, only n=42 yields one for all n up to 7700.
%o (PARI) is(n)=ispseudoprime(n*10^n+n-1) \\ _Charles R Greathouse IV_, Jun 13 2017
%A _Jason Earls_, Sep 07 2005