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 A069605 #13 Dec 15 2017 17:35:51
%S A069605 3,1,1,9,3,17,1,3,9,39,33,53,1,21,27,113,99,123,3,91,39,29,141,87,67,
%T A069605 297,87,333,59,67,509,103,279,99,141,107,9,1,123,83,529,521,517,137,
%U A069605 249,459,543,583,513,21,53,1029,657,219,313,17,237,19,689,339,307,23
%N A069605 a(1) = 3; a(n) = smallest number such that the concatenation a(1)a(2)...a(n) is a prime.
%e A069605 a(6) = 17 and the number 3119317 is a prime.
%t A069605 a[1] = 3; a[n_] := a[n] = Block[{k = 1, c = IntegerDigits @ Table[ a[i], {i, n - 1}]}, While[ !PrimeQ[ FromDigits @ Flatten @ Append[c, IntegerDigits[k]]], k += 2]; k]; Table[ a[n], {n, 63}] (* _Robert G. Wilson v_, Aug 05 2005 *)
%Y A069605 Cf. A033681, A074339, A092528, A069603, A069605, A069606, A069607, A069608, A069609, A069610, A069611, A111525.
%K A069605 nonn,base
%O A069605 1,1
%A A069605 _Amarnath Murthy_, Mar 26 2002
%E A069605 More terms from _Jason Earls_, Jun 13 2002