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 A032650 #30 Nov 25 2021 09:31:39 %S A032650 33,99,2121,2323,5151,5959,6363,7171,7575,8787,8989,9999,105105, %T A032650 111111,117117,123123,129129,135135,143143,147147,153153,171171, %U A032650 173173,177177,191191,201201,237237,243243,255255,263263,285285,305305,309309,317317 %N A032650 Lucky numbers that are concatenations of a number k with itself. %H A032650 Kevin P. Thompson, <a href="/A032650/b032650.txt">Table of n, a(n) for n = 1..4215</a> (first 95 terms from Amiram Eldar) %F A032650 a(n) = A032640(n) || A032640(n), where || denotes concatenation. - _Kevin P. Thompson_, Nov 09 2021 %Y A032650 Intersection of A000959 and A020338. %Y A032650 Cf. A032640. %K A032650 nonn,base %O A032650 1,1 %A A032650 _Patrick De Geest_, May 15 1998 %E A032650 More terms from _Sascha Kurz_, Mar 24 2002 %E A032650 Edited by _Charles R Greathouse IV_, Apr 26 2010