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A307331 The number of Ulam numbers below 10^n. 0
6, 26, 125, 827, 7584, 74083, 740368, 7399353, 73976842, 739778038, 7397814233, 73979274540 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 19 12:52 EST 2020. Contains 331049 sequences. (Running on oeis4.)