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A194850 Number of prefix normal words of length n. 3
2, 3, 5, 8, 14, 23, 41, 70, 125, 218, 395, 697, 1273, 2279, 4185, 7568, 13997, 25500, 47414, 87024, 162456, 299947, 562345, 1043212, 1962589, 3657530, 6900717, 12910042, 24427486, 45850670, 86970163, 163756708, 311283363, 587739559, 1119581278, 2119042830 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A binary word of length n is prefix normal if for all 1 <= k <= n, no factor of length k has more a's than the prefix of length k. That is, abbabab is not prefix normal because aba has more a's than abb. - Zsuzsanna Liptak, Oct 12 2011

a(n) <= A062692(n): every prefix normal word is a pre-necklace, but the converse is not true, see the Fici/Lipták reference. - Joerg Arndt, Jul 20 2013

LINKS

Zsuzsanna Liptak, Table of n, a(n) for n = 1..50

P. Burcsi, G. Fici, Zs. Lipták, F. Ruskey, and J. Sawada, On Combinatorial Generation of Prefix Normal Words, arXiv:1401.6346 [cs.DS]

P. Burcsi, G. Fici, Z. Lipták, F. Ruskey, J. Sawada, Normal, Abby Normal, Prefix Normal, arXiv preprint arXiv:1404.2824, 2014

Péter Burcsi, Gabriele Fici, Zsuzsanna Lipták, Frank Ruskey, Joe, On Prefix Normal Words and Prefix Normal Forms, arXiv:1611.09017 [cs.DM], (2016)

G. Fici and Zs. Lipták, On Prefix Normal Words

G. Fici and Zs. Lipták, On Prefix Normal Words, Developments in Language Theory 2011, Lecture Notes in Computer Science 6795, 228-238.

EXAMPLE

For n=3: aaa, aab, abb, aba, bbb are all prefix normal words. - Zsuzsanna Liptak, Oct 12 2011

CROSSREFS

Cf. A062692 (binary pre-necklaces).

See A238109 for a list of the prefix-normal words.

Sequence in context: A005627 A191794 A191388 * A062692 A182024 A086661

Adjacent sequences:  A194847 A194848 A194849 * A194851 A194852 A194853

KEYWORD

nonn

AUTHOR

Gabriele Fici, Sep 04 2011

EXTENSIONS

More terms added by Zsuzsanna Liptak, Oct 12 2011

Further terms added by Zsuzsanna Liptak, Jan 29 2014

STATUS

approved

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Last modified September 25 21:33 EDT 2017. Contains 292500 sequences.