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 A029984 #29 Feb 10 2025 23:55:58
%S A029984 0,1,2,4,10,11,20,22,28,34,56,82,89,113,154,164,244,262,488,524,730,
%T A029984 755,802,862,1021,1342,1358,1460,2188,2242,2684,2716,3046,4276,4376,
%U A029984 4484,6562,6641,6778,8030,8215,8350,8887,12482,13124,14810,19684
%N A029984 Numbers k such that k^2 is palindromic in base 3.
%H A029984 Giovanni Resta, <a href="/A029984/b029984.txt">Table of n, a(n) for n = 1..400</a> (first 100 terms from Harvey P. Dale)
%H A029984 Patrick De Geest, <a href="https://www.worldofnumbers.com/nobase10pg2.htm">Palindromic Squares in bases 2 to 17</a>
%H A029984 G. J. Simmons, <a href="/A002778/a002778.pdf">On palindromic squares of non-palindromic numbers</a>, J. Rec. Math., 5 (No. 1, 1972), 11-19. [Annotated scanned copy]
%t A029984 pal3Q[n_]:=Module[{idn3=IntegerDigits[n^2,3]},idn3==Reverse[idn3]]; Select[Range[0,20000],pal3Q] (* _Harvey P. Dale_, May 22 2012 *)
%Y A029984 Cf. A002778, A003166, A007089, A029985, A263607, A263608.
%K A029984 nonn,base
%O A029984 1,3
%A A029984 _Patrick De Geest_