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 A069603 #20 May 11 2023 12:46:12
%S A069603 2,3,3,3,3,21,17,3,13,99,17,3,7,77,19,119,7,33,29,49,149,43,23,99,9,
%T A069603 31,57,93,29,21,91,59,31,39,87,11,121,231,279,269,51,21,313,297,527,
%U A069603 309,27,21,67,63,431,231,13,99,407,453,69,409,189,11,31,21,23,19,93,1143
%N A069603 a(1) = 2; a(n) = smallest number such that the juxtaposition a(1)a(2)...a(n) is a prime.
%H A069603 Michael S. Branicky, <a href="/A069603/b069603.txt">Table of n, a(n) for n = 1..1000</a> (terms 1..100 from Zak Seidov)
%e A069603 a(6) = 21 and the number 2333321 is a prime.
%t A069603 a[1] = 2; 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, 67}] (* _Robert G. Wilson v_, Aug 05 2005 *)
%o A069603 (Python)
%o A069603 from gmpy2 import is_prime
%o A069603 from itertools import count, islice
%o A069603 def agen(): # generator of terms
%o A069603 an, s = 2, "2"
%o A069603 while True:
%o A069603 yield an
%o A069603 an = next(k for k in count(3, 2) if is_prime(int(s+str(k))))
%o A069603 s += str(an)
%o A069603 print(list(islice(agen(), 66))) # _Michael S. Branicky_, May 11 2023
%Y A069603 Cf. A033679, A074338, A092528, A069605, A069606, A069607, A069608, A069609, A069610, A069611, A111525.
%K A069603 nonn,base
%O A069603 1,1
%A A069603 _Amarnath Murthy_, Mar 26 2002
%E A069603 More terms from _Jason Earls_, Jun 13 2002