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 A032640 #24 Nov 25 2021 09:31:43 %S A032640 3,9,21,23,51,59,63,71,75,87,89,99,105,111,117,123,129,135,143,147, %T A032640 153,171,173,177,191,201,237,243,255,263,285,305,309,317,327,357,363, %U A032640 369,371,387,389,393,431,443,459,465,467,495,497,513,521,533,561,567,573 %N A032640 Numbers k such that k concatenated with itself is a lucky number. %H A032640 Kevin P. Thompson, <a href="/A032640/b032640.txt">Table of n, a(n) for n = 1..4215</a> (first 95 terms from Amiram Eldar) %e A032640 123 is a member of the sequence since 123123 is a lucky number, i.e. A000959(10590) = 123123. %Y A032640 Cf. A000959, A032650. %K A032640 nonn,base %O A032640 1,1 %A A032640 _Patrick De Geest_, May 15 1998 %E A032640 More terms from _Sascha Kurz_, Mar 24 2002