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 A056544 #15 Apr 14 2021 22:40:33
%S A056544 1,2,3,4,5,6,7,8,9,101,11,121,131,141,151,161,171,181,191,202,121,22,
%T A056544 232,242,252,262,272,282,292,303,131,232,33,343,353,363,373,383,393,
%U A056544 404,141,242,343,44,454,464,474,484,494,505,151,252,353,454,55,565,575
%N A056544 Smallest palindrome containing the digits of n as a subsequence.
%H A056544 Rémy Sigrist, <a href="/A056544/b056544.txt">Table of n, a(n) for n = 1..10000</a>
%H A056544 Rémy Sigrist, <a href="/A056544/a056544.gp.txt">PARI program for A056544</a>
%F A056544 a(A002113(n)) = A002113(n). - _Chai Wah Wu_, Apr 13 2021
%e A056544 The smallest palindrome containing 21 as a subsequence is 121. So a(21) = 121.
%t A056544 Do[k = 1; While[ StringPosition[ ToString[k], ToString[n]] == {} || ToString[k] != StringReverse[ ToString[k]], k++ ]; Print[k], {n, 1, 70} ]
%o A056544 (PARI) See Links section.
%Y A056544 Cf. A002113, A082216, A145800 (binary variant).
%K A056544 base,easy,nonn
%O A056544 1,2
%A A056544 _Joseph L. Pe_, Feb 10 2002
%E A056544 Edited and extended by _Robert G. Wilson v_, Feb 12 2002