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 A347680 #24 Dec 31 2023 12:35:45
%S A347680 3,23,3323,233323,22223233323233323,
%T A347680 223333322323332323332322223233323233323,
%U A347680 3322233323332323332322223233323233323223333322323332323332322223233323233323
%N A347680 Beginning with 3, least prime > a(n-1) using only digits 2 and 3 such that every concatenation a(1),a(2),... is a palindrome.
%C A347680 a(11) has 1258 decimal digits.
%H A347680 Chai Wah Wu, <a href="/A347680/b347680.txt">Table of n, a(n) for n = 1..10</a>
%e A347680 3, 323, 3233323,... are all palindromes.
%t A347680 a[1]=3;a[n_]:=a[n]=(t=1;While[!IntegerQ[k=Min[FromDigits/@Select[Select[Tuples[{2,3},t],PrimeQ@FromDigits@#&],PalindromeQ@FromDigits@Flatten[{IntegerDigits/@Array[a,n-1],#}]&]]]||k<=a[n-1],t++];k);Array[a,5] (* _Giorgos Kalogeropoulos_, Sep 15 2021 *)
%Y A347680 Cf. A002113.
%K A347680 nonn,base
%O A347680 1,1
%A A347680 _N. J. A. Sloane_ and _Chai Wah Wu_, Sep 15 2021