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%I #42 Mar 28 2018 22:02:03
%S 6,11,14,16,18,21
%N Numbers that are not differences between successive Ulam numbers (A002858).
%C Unfortunately, it appears that the entries are all conjectural. I am not aware of any proofs that the listed numbers can never appear. The terms shown are those listed by Pickover. - _N. J. A. Sloane_, Jun 19 2008
%C However, a gap of 35 doesn't occur until after the 35755308th term (483379914), so these missing gaps could eventually occur. - _Jud McCranie_, Jun 13 2008
%C The sequence is conjectured to continue: 23, 26, 28, 31, 33. These gaps do not appear in the first 158000000 terms, so are candidates for the sequence. [_Jud McCranie_, Sep 12 2013]
%C The conjectured list of gaps that don't appear holds through the first 28 billion Ulam numbers. - _Jud McCranie_, Jan 07 2016
%D Clifford A. Pickover, "Wonders of Numbers, ...", Oxford University Press, 2000
%H Philip Gibbs, Judson McCranie, <a href="https://www.researchgate.net/profile/Philip_Gibbs/publication/320980165_The_Ulam_Numbers_up_to_One_Trillion/links/5a058786aca2726b4c78588d/The-Ulam-Numbers-up-to-One-Trillion.pdf">The Ulam Numbers up to One Trillion</a>, (2017).
%H C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," <a href="http://www.zentralblatt-math.org/zmath/en/search/?q=an:0983.00008&format=complete">Zentralblatt review</a>
%Y Cf. A002858, A072832.
%K more,nonn,hard
%O 1,1
%A _Benoit Cloitre_, Aug 04 2002
%E Edited by _Max Alekseyev_, Dec 19 2011
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