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 A080241 #13 Mar 10 2015 04:41:07
%S A080241 0,1,3,7,13,27,55,109,219,437,875,1751,3501,7003,14005,28011,56021,
%T A080241 112043,224085,448171,896341,1792683,3585365,7170731,14341463,
%U A080241 28682925,57365851,114731701,229463403,458926805,917853611,1835707221
%N A080241 Define two sequences by A_n = mex{A_i,B_i : 0 <= i < n} for n >= 0, B_0=0, B_1=1 and for n >= 2, B_n = 2B_{n-1}+(-1)^{A_n}. Sequence gives B_n.
%C A080241 The minimal excluded value of set of nonnegative numbers S is mex S = least nonnegative integer not in S.
%C A080241 The sequence A_n is given in A080240.
%H A080241 A. S. Fraenkel, <a href="http://www.wisdom.weizmann.ac.il/~fraenkel/">Home Page</a>
%H A080241 A. S. Fraenkel, <a href="http://www.emis.de/journals/INTEGERS/papers/eg6/eg6.Abstract.html">New games related to old and new sequences</a>, INTEGERS, Electronic J. of Combinatorial Number Theory, Vol. 4, Paper G6, 2004.
%Y A080241 Cf. A080240.
%K A080241 nonn
%O A080241 0,3
%A A080241 _Aviezri S. Fraenkel_, Mar 12 2003
%E A080241 More terms from _John W. Layman_, May 04 2004