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 A223089 #4 Mar 23 2013 05:10:18
%S A223089 1015,11165,102515,112665,1016015,1127665,10151015,10252515,11176165,
%T A223089 11277665,101501015,102617515,111661165,112777665,1015001015,
%U A223089 1016016015,1025252515,1026267515,1116511165,1117526165,1126762665,1127777665
%N A223089 Numbers n, written in base 8, with the property that if the base-8 representation of n is read backwards, the result is 5*n.
%C A223089 For the decimal representations of these numbers, see A217742.
%C A223089 Theorem: There are 2^{floor(d/2)-2} terms with d base-8 digits.
%e A223089 1015 reversed is 5101 = 5*1015 (calculating in base 8).
%Y A223089 Cf. A214927, A217742.
%K A223089 nonn,base
%O A223089 1,1
%A A223089 _N. J. A. Sloane_, Mar 23 2013