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 A083980 #12 Mar 25 2019 11:36:26
%S A083980 191,919,19991,1993991,9199919,199909991,199999991,90999599909,
%T A083980 95999999959,99999199999,9599999999959,199999959999991,
%U A083980 959999999999959,39999999299999993,94999999999999949,99999999299999999,9299999999999999929,9999999992999999999
%N A083980 Smallest palindromic prime containing exactly n 9's.
%H A083980 Chai Wah Wu, <a href="/A083980/b083980.txt">Table of n, a(n) for n = 1..500</a>
%t A083980 Table[d = 9; i = 1;
%t A083980 While[ x = IntegerDigits[Prime[i]];
%t A083980 x != Reverse[x] || Count[x, d] != n , i++];
%t A083980 FromDigits[x], {n, 1, 5}] (* _Robert Price_, Mar 25 2019 *)
%Y A083980 Cf. A083972, A083973, A083974, A083975, A083976, A083977, A083978, A083979, A083981.
%K A083980 base,nonn
%O A083980 1,1
%A A083980 _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 21 2003
%E A083980 Corrected and extended by _Giovanni Resta_, Feb 08 2006