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%I #11 Apr 04 2019 18:25:13
%S 6,26,125,827,7584,74083,740368,7399353,73976842,739778038,7397814233,
%T 73979274540
%N The number of Ulam numbers below 10^n.
%C The terms a(1)-a(12) are from the paper by Gibbs and McCranie.
%C The number of Ulam numbers not exceeding 10^n can be calculated from this sequence using the fact that up to 10^12 the only powers of 10 that are Ulam numbers are 10^6 and 10^11.
%C The asymptotic density D of Ulam numbers is known to be 0 <= D <= 0.4. Gibbs and McCranie estimated it from this sequence as ~ 0.073979.
%H Philip Gibbs, Judson McCranie, <a href="https://www.researchgate.net/publication/320980165_The_Ulam_Numbers_up_to_One_Trillion">The Ulam Numbers up to One Trillion</a>, (2017).
%Y Cf. A002858.
%K nonn,more
%O 1,1
%A _Amiram Eldar_, Apr 02 2019