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 A247341 #9 Sep 17 2014 15:54:13
%S A247341 1,1,1,1,1,4,1,1,2,3,1,1,4,4,6,30,3,1,6,1,32,3,3,2,22,1,6,1,2,14,7,1,
%T A247341 10,1,2,6,3,4,2,5,2,6,1,1,37,53,53,13,64,1,67,1,45,29,17,12,14,1,2,5,
%U A247341 15,36,10,7,1,1,81,4,18,5,55,8,33,19,8,6,2,11
%N A247341 Let b_k=3...3 consist of k>=1 3's. Then a(n) is the smallest k such that the concatenation 2^n b_k is prime, or a(n)=0 if there is no such prime.
%C A247341 Conjecture: for all n, a(n)>0.
%o A247341 (PARI) a(n) = {k = 0; while (! isprime(eval(concat(Str(2^n), Str((10^k-1)/3)))), k++); k;} \\ _Michel Marcus_, Sep 16 2014
%Y A247341 Cf. A000079, A232210, A242775.
%K A247341 nonn
%O A247341 0,6
%A A247341 _Vladimir Shevelev_, Sep 14 2014
%E A247341 More terms from _Michel Marcus_, Sep 16 2014