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 A033681 #11 Mar 02 2015 03:07:23
%S A033681 3,7,9,51,51,51,97,131,157,159,243,309,327,363,383,411,487,639,873,
%T A033681 983,1231,1257,1337,1549,1589,2101,2159,2317,2871,2907,4053,4097,4597,
%U A033681 4703,5559,5799,6337,6527,6561,6939,7147,7167,7839,8403,8873,9237,9541,9771
%N A033681 a(1) = 3; a(n) is smallest number >= a(n-1) such that the juxtaposition a(1)a(2)...a(n) is a prime.
%t A033681 a[1] = 3; a[n_] := a[n] = Block[{k = a[n - 1], c = IntegerDigits @ Table[ a[i], {i, n - 1}]}, While[ !PrimeQ[ FromDigits @ Flatten @ Append[c, IntegerDigits[k]]], k += 2]; k]; Table[ a[n], {n, 48}] (* _Robert G. Wilson v_ *)
%Y A033681 Cf. A069605, A074339, A033680, A033679, A046254, A046255, A046256, A046257, A046258, A046259, A111524.
%K A033681 nonn
%O A033681 1,1
%A A033681 _N. J. A. Sloane_
%E A033681 More terms from _Patrick De Geest_, May 15 1998
%E A033681 More terms from _Robert G. Wilson v_, Aug 05 2005