This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A068714 #10 Dec 05 2013 19:55:12
%S A068714 23,29,227,281,2243,2729,26561,219683,24782969,210460353203,
%T A068714 2282429536481,27625597484987,250031545098999707,
%U A068714 279766443076872509863361,2239299329230617529590083,219383245667680019896796723,2202755595904452569706561330872953769
%N A068714 Primes formed from a concatenation of 2 and 3^k for some k.
%e A068714 2243 is a member as it is a concatenation of 2 and 243 = 3^5.
%t A068714 Select[Table[FromDigits[Prepend[IntegerDigits[3^n],2]],{n,75}],PrimeQ] (* _Jayanta Basu_, May 22 2013 *)
%Y A068714 Cf. A068712.
%K A068714 nonn,base
%O A068714 0,1
%A A068714 _Amarnath Murthy_, Mar 05 2002
%E A068714 More terms from _Sascha Kurz_, Mar 17 2002