

A181047


Number of lengthn sequences A over {1,2,3} with the property that all of r(A), r(r(A)), etc. are over {1,2,3}, where r is the sequence obtained by taking the run lengths in A.


0



1, 3, 9, 27, 54, 180, 426, 1080, 2724, 6300, 16512, 42432, 98064, 248256, 616656, 1509888, 3767040
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OFFSET

0,2


LINKS

Table of n, a(n) for n=0..16.


EXAMPLE

For example, the runlengths in 1333 are 13, then the runlengths of this is 11, then the runlengths of this is 2, then the runlengths of this is 1, so this sequence is counted in a(4).


CROSSREFS

Sequence in context: A163791 A248078 A057829 * A014948 A093665 A093546
Adjacent sequences: A181044 A181045 A181046 * A181048 A181049 A181050


KEYWORD

nonn,hard


AUTHOR

Jeffrey Shallit, Oct 01 2010


EXTENSIONS

a(0)a(10) confirmed and a(11)a(14) added by John W. Layman, Oct 07 2010
a(15)a(16) from Alois P. Heinz, Oct 16 2011


STATUS

approved



