OFFSET
1,1
COMMENTS
The terms a(1)-a(12) are from the paper by Gibbs and McCranie.
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.
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.
LINKS
Philip Gibbs, Judson McCranie, The Ulam Numbers up to One Trillion, (2017).
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Apr 02 2019
STATUS
approved