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Numbers n such that 4(10^n-1)/9 * 10^ceiling(log_10(n+1)) + n is prime.
2

%I #2 Mar 30 2012 17:36:45

%S 1,547,1187,11183

%N Numbers n such that 4(10^n-1)/9 * 10^ceiling(log_10(n+1)) + n is prime.

%C No term is a multiple of 2, 3, or 5. The decimal expansion of each corresponding prime is n 4's with n's decimal expansion concatenated. Probable primes found by PrimeForm. Primes for 547 and 1187 proved by Primo. No more terms up to 30000.

%e The first term is 1 because 41 is prime.

%Y Cf. n k's followed by n is prime: A070746 (k=1), A176087 (k=3), A176090 (k=6), A084428 (k=7), A176091 (k=9). [k=2, 5, and 8 produce only composites divisible by 3.]

%K more,nonn

%O 1,2

%A _Rick L. Shepherd_, Apr 11 2010