A181047 - OEIS

A181047

Number of length-n 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.

%I #11 May 25 2013 01:50:23

%S 1,3,9,27,54,180,426,1080,2724,6300,16512,42432,98064,248256,616656,

%T 1509888,3767040

%N Number of length-n 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.

%e For example, the run-lengths in 1333 are 13, then the run-lengths of this is 11, then the run-lengths of this is 2, then the run-lengths of this is 1, so this sequence is counted in a(4).

%K nonn,hard

%O 0,2

%A _Jeffrey Shallit_, Oct 01 2010

%E a(0)-a(10) confirmed and a(11)-a(14) added by _John W. Layman_, Oct 07 2010

%E a(15)-a(16) from _Alois P. Heinz_, Oct 16 2011