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 A102499 #10 Dec 17 2023 16:12:05
%S A102499 313133,323233,328283,329293,338383,343433,349493,350503,352523,
%T A102499 356563,364643,367673,380803,383833,392923,394943,395953,397973,
%U A102499 3100010003,3100310033,3102410243,3102510253,3102810283,3103910393,3104610463
%N A102499 Primes of the concatenated form 3nn3.
%e A102499 313133 is prime and of the form 3nn3 for n=13.
%e A102499 3100010003 is prime and of the form 3nn3 for n=1000.
%t A102499 mn[n_]:=Module[{idn=IntegerDigits[n]}, FromDigits[Join[{3},idn,idn,{3}]]]; Select[ mn/@ Range[ 1100],PrimeQ] (* _Harvey P. Dale_, Feb 04 2011 *)
%Y A102499 Cf. A102896 for sequence of all numbers of form 3nn3. A102498 for the n values corresponding to the primes in this sequence.
%K A102499 easy,nonn,base
%O A102499 1,1
%A A102499 Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005