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 A288850 #16 Jun 20 2017 23:29:55
%S A288850 1,3,6,16,58,321,2585,30198
%N A288850 Number of distinct nonnegative rational numbers that can be obtained in n steps by a straight-line program (SLP) starting at 1 using addition, subtraction, multiplication and division.
%H A288850 Hugo Pfoertner, <a href="/A288850/a288850.pdf">Distribution of values generated by n-step SLPs</a>, Illustration.
%e A288850 The sets of numbers obtainable at the n-th step are:
%e A288850 S(0) = { 1 },
%e A288850 S(1) = { 0, 1, 2 },
%e A288850 S(2) = { 0, 1/2, 1, 2, 3, 4 },
%e A288850 S(3) = { 0, 1/4, 1/3, 1/2, 2/3, 1, 3/2, 2, 5/2, 3, 4, 5, 6, 8, 9, 16 }.
%Y A288850 Cf. A216999, A288760, A288849.
%K A288850 nonn,hard,more
%O A288850 0,2
%A A288850 _Hugo Pfoertner_, Jun 18 2017
%E A288850 a(7) from _Alois P. Heinz_, Jun 18 2017