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 A121939 #2 Mar 30 2012 18:49:08
%S A121939 1,2,3,4,5,6,7,8,9,919,1881,8118,9229,10801,11711,12621,13531,14441,
%T A121939 15351,16261,17171,18081,21612,25152,27972,28882,29792,31513,33133,
%U A121939 41014,41114,41214,41314,41414,41514,41614,41714,41814,41914,51315
%N A121939 Palindromic numbers that contain the sum of their digits as a substring.
%t A121939 Select[Table[n, {n, 100000}], Length[StringPosition[ToString[ # ], ToString[Plus @@ IntegerDigits[ # ]]]] > 0 && ToString[ # ] == StringReverse[ToString[ # ]] &]
%Y A121939 Cf. Palindromic subsequence of A052018 - Sum of digits of n is substring of n.
%K A121939 nonn,base
%O A121939 1,2
%A A121939 _Tanya Khovanova_, Sep 03 2006