A109445 - OEIS

%I #3 Oct 02 2013 15:12:46

%S 4,8,10,42,452,1014

%N Numbers n such that (concatenation of even integers through n) - 1 is a prime.

%C Next term is greater than 2000. All terms less than 1000 correspond to certified primes (Primo 2.2.0 beta).

%e 4 is a term because 24 - 1 = 23 is prime.

%e 8 is a term because 2468 - 1 = 2467 is prime.

%t p = ""; Do[p = p <> ToString[2*n]; If[PrimeQ[ToExpression[p] - 1], Print[2*n]], {n, 1, 10^3}]

%Y Cf. A066811.

%K base,nonn

%O 1,1

%A _Ryan Propper_, Aug 26 2005