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 A219906 #14 Sep 28 2017 17:22:05
%S A219906 1,3,13,82,788,12141,302791,11729499
%N A219906 Number of different straight line programs of length n.
%C A219906 See Borwein and Hobart (or A216999) for definition.
%H A219906 Peter Borwein and Joe Hobart, <a href="http://www.jstor.org/stable/10.4169/amer.math.monthly.119.07.584">The extraordinary power of division in straight line programs</a>, American Mathematical Monthly 119:7 (2012), pp. 584-592.
%p A219906 g:= f-> seq([f[], t], t={seq(seq({i+j, i-j, i*j}[], j=f), i=f)}):
%p A219906 F:= proc(n) F(n):= map(g, F(n-1)) end: F(0):= {[1]}:
%p A219906 a:= n-> nops(F(n)):
%p A219906 seq(a(n), n=0..5); # _Alois P. Heinz_, Dec 14 2012
%Y A219906 Cf. A173419, A216999, A217032.
%K A219906 nonn,more
%O A219906 0,2
%A A219906 _N. J. A. Sloane_, Dec 13 2012
%E A219906 Typo in a(4) corrected, a(6)-a(7) from _Alois P. Heinz_, Dec 14 2012