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 A046254 #9 Jul 19 2015 00:36:28
%S A046254 4,7,9,9,39,47,57,81,111,123,243,283,287,313,407,507,807,1057,1209,
%T A046254 1211,1443,1447,1619,2019,2269,2429,2637,2679,2751,3007,3287,3789,
%U A046254 3829,3833,3949,4151,4533,4821,5097,5331,5457,5529,5691,6021,6153,6393,6409
%N A046254 a(1) = 4; a(n) is smallest number >= a(n-1) such that the juxtaposition a(1)a(2)...a(n) is a prime.
%t A046254 a[1] = 4; 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 ++ ]; k]; Table[ a[n], {n, 47}] (* _Robert G. Wilson v_, Aug 05 2005 *)
%Y A046254 Cf. A069606, A074340, A033680, A033679, A033681, A046255, A046256, A046257, A046258, A046259, A111524.
%K A046254 nonn
%O A046254 1,1
%A A046254 _Patrick De Geest_, May 15 1998