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 A082723 #9 Aug 11 2024 14:41:34
%S A082723 1,9,111,474,969,6666,18981,67276,4411144,6964696,15444451,57966975,
%T A082723 448707844,460595064,579696975,931929139,994040499,1227667221,
%U A082723 9698998969,61556965516,664248842466,699030030996,99451743334715499
%N A082723 Palindromic nonagonal (or 9-gonal or enneagonal) numbers.
%H A082723 P. De Geest, <a href="https://www.worldofnumbers.com/nona.htm">Palindromic nonagonals</a>
%t A082723 palQ[n_]:=Module[{idn=IntegerDigits[n]},idn==Reverse[idn]]; Select[Table[ (n(7n-5))/2,{n,170000000}],palQ] (* _Harvey P. Dale_, Nov 15 2011 *)
%Y A082723 Cf. A001106, A055560.
%K A082723 nonn,base
%O A082723 1,2
%A A082723 _Patrick De Geest_, Apr 13 2003