A072540 Numbers that are not differences between successive Ulam numbers (A002858).

6, 11, 14, 16, 18, 21

Offset

1,1

Comments

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

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

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]

The conjectured list of gaps that don't appear holds through the first 28 billion Ulam numbers. - Jud McCranie, Jan 07 2016

References

Clifford A. Pickover, "Wonders of Numbers, ...", Oxford University Press, 2000

Links

Table of n, a(n) for n=1..6.

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

C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review

Crossrefs

Cf. A002858, A072832.

Sequence in context: A201915 A237606 A264935 * A315374 A315375 A315376

Adjacent sequences: A072537 A072538 A072539 * A072541 A072542 A072543

Keyword

more,nonn,hard

Author

Benoit Cloitre, Aug 04 2002

Extensions

Edited by Max Alekseyev, Dec 19 2011

Status

approved