A307331 The number of Ulam numbers below 10^n.

6, 26, 125, 827, 7584, 74083, 740368, 7399353, 73976842, 739778038, 7397814233, 73979274540

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

Table of n, a(n) for n=1..12.

Philip Gibbs, Judson McCranie, The Ulam Numbers up to One Trillion, (2017).

Crossrefs

Cf. A002858.

Sequence in context: A283341 A046647 A233075 * A298625 A046233 A140231

Adjacent sequences: A307328 A307329 A307330 * A307332 A307333 A307334

Keyword

nonn,more

Author

Amiram Eldar, Apr 02 2019

Status

approved