%I #2 Mar 30 2012 17:36:45
%S 307,1759,2963,3881
%N Numbers n such that (10^n-1) * 10^ceiling(log_10(n+1)) + n is prime.
%C No term is a multiple of 2, 3, or 5. (In fact, a(1) through a(4) are prime.) The decimal expansion of each corresponding prime is n 9's with n's decimal expansion concatenated. Probable primes found by PrimeForm. Primes for 307 and 1759 proved by Primo. No more terms up to 30000.
%Y Cf. A174352 (n followed by n 9's is prime), n k's followed by n is prime: A070746 (k=1), A176087 (k=3), A176089 (k=4), A176090 (k=6), A084428 (k=7). [k=2, 5, and 8 produce only composites divisible by 3.]
%K more,nonn
%O 1,1
%A _Rick L. Shepherd_, Apr 16 2010