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 A181720 #22 Apr 07 2020 21:57:23
%S A181720 1,2,3,4,5,6,7,8,9,1010,11,216,312,1414,510,1616,714,810,912,1020,126,
%T A181720 22,322,2424,525,624,729,1820,928,3030,713,2304,33,3434,3535,3636,
%U A181720 1073,836,936,1040,1148,924,344,44,540,644,1974,384,294,1050,153,2548,3551,1458,55,5656,4275,1856,295,3060
%N A181720 a(n) = smallest multiple of n which contains its base 10 reversal as a substring.
%C A181720 Leading 0's are kept in the reversal: e.g., a(10)=1010, not 10.
%H A181720 Ivan Neretin, <a href="/A181720/b181720.txt">Table of n, a(n) for n = 1..10000</a>
%o A181720 (Perl) foreach $n(1..60) {$r=reverse($_=$n); $_+=$n until m/$r/; print "$n $_\n"} # _Ivan Neretin_, Aug 12 2015
%Y A181720 Cf. A181721 (a(n)/n).
%K A181720 nonn,base
%O A181720 1,2
%A A181720 _Claudio Meller_, Nov 17 2010
%E A181720 Edited by _D. S. McNeil_, Nov 17 2010