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 A055157 #9 Aug 16 2019 22:29:01 %S A055157 495,6174,97508421,864197532,9753086421 %N A055157 n has distinct digits and n=a-b where a has the digits of n in descending order and b has the digits of n in ascending order (perhaps with leading zeros). %H A055157 Dennis Borris, <a href="https://web.archive.org/web/20060917004138/http://www.ecst.csuchico.edu/~kend/potw/archive/000420sol.html">Identity by Ordered Subtraction</a>, Ken Duisenberg's Puzzle of the Week, April 20, 2000. %F A055157 a(n) = A055158(n) - A055159(n). %e A055157 495 = 954-459. %Y A055157 Cf. A055158, A055159, A055160. %K A055157 nonn,base,fini,full %O A055157 0,1 %A A055157 _Henry Bottomley_, Apr 27 2000