|
%I #4 Jun 13 2017 10:22:44
%S 1,2,275,1556
%N Numbers n such that n*10^n + (10^n - 1)/3 is prime.
%C No term is a multiple of 3. The decimal expansion of each corresponding prime is n's decimal expansion with n 3's concatenated. Primes and probable primes found by PrimeForm. Primes for 275 and 1556 proved by Primo. No more terms up to 30000.
%e The numbers 1 and 2 are terms because 13 and 233 are prime.
%o (PARI) is(n)=ispseudoprime(n*10^n+(10^n-1)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A068817 (n followed by n 1's is prime), A133127 (n followed by n 7's is prime), A174352 (n followed by n 9's is prime).
%K more,nonn
%O 1,2
%A _Rick L. Shepherd_, Mar 27 2010
| 