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 A101620 #5 Mar 29 2014 13:57:19
%S A101620 1,3,9,11,13,15,129,131,133,137,139,141,143,145,153,161,163,165,171,
%T A101620 175,177,179,187,193,195,197,205,207,209,213,221,241,243,245,255
%N A101620 Decimal encoding of digraph topologies.
%C A101620 The sequence encodes labeled digraph topologies as described by and counted in A000798.
%e A101620 Let a = 2, b = 4, c = 16, d = 256, ...
%e A101620 a(19) = 171 because we can map { }, a, ab, ac, abc to 1 + 2 + 8 + 32 + 128
%e A101620 Viewed as an array the table begins
%e A101620 1
%e A101620 3
%e A101620 9 11 13 15
%e A101620 129 131 133 137 139 141 143 145 153 161 163 165 171 175 177 ...
%e A101620 with respectively 1 1 4 29 355 ... (A000798) entries on each row.
%Y A101620 Cf. A000798, A001035, A001930, A074486.
%K A101620 more,nonn,tabf,base
%O A101620 1,2
%A A101620 _Alford Arnold_, Dec 10 2004