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 A104340 #8 Oct 28 2017 17:25:07 %S A104340 12,23,34,45,56,67,78,89 %N A104340 Numbers n such that (digital reversal of n) - n = 9. %C A104340 The sequence is complete: there is no other such number (in base 10). %H A104340 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/NonRecursions.html">Non Recursions</a> %e A104340 98-89=9 %t A104340 Select[Range[1000],FromDigits[Reverse[IntegerDigits[#]]]-#==9&] (* _Harvey P. Dale_, Aug 26 2011 *) %t A104340 Select[Range[1000],IntegerReverse[#]-#==9&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Oct 28 2017 *) %Y A104340 Cf. A104341. %K A104340 base,nonn,fini,full %O A104340 1,1 %A A104340 _Zak Seidov_, Mar 02 2005