%I #10 Feb 24 2021 02:48:18
%S 1,1,3,1,3,3,7,3,3,3,7,5,7,9,17,9,3,3,7,5,7,9,17,11,7,9,17,17,19,23,
%T 39,27,7,3,7,5,7,9,17,11,7,9,17,17,19,23,39,29,11,9,17,17,19,25,43,39,
%U 25,23,39,45,47,57,93,77,23,3,7,5,7,9
%N a(n) = A160121(n+1)/3.
%C Also, first differences of A161910. [From _Omar E. Pol_, Jun 21 2009]
%H David Applegate, Omar E. Pol and N. J. A. Sloane, <a href="/A000695/a000695_1.pdf">The Toothpick Sequence and Other Sequences from Cellular Automata</a>, Congressus Numerantium, Vol. 206 (2010), 157-191. [There is a typo in Theorem 6: (13) should read u(n) = 4.3^(wt(n-1)-1) for n >= 2.]
%H N. J. A. Sloane, <a href="/wiki/Catalog_of_Toothpick_and_CA_Sequences_in_OEIS">Catalog of Toothpick and Cellular Automata Sequences in the OEIS</a>
%e Note that this can be written as a triangle:
%e 1;
%e 1;
%e 3;
%e 1,3;
%e 3,7,3,3;
%e 3,7,5,7,9,17,9,3;
%e 3,7,5,7,9,17,11,7,9,17,17,19,23,39,27,7;
%e 3,7,5,7,9,17,11,7,9,17,17,19,23,39,29,11,9,17,17,19,25,43,39,25,23,39,45,47,57,93,77,23;
%e 3,7,5,7,9,...
%Y Y-toothpick sequence: A160120. Cf. A160121, A160122.
%Y Cf. A139250, A139251. [From _Omar E. Pol_, Jun 16 2009]
%Y Cf. A161831, A161427, A161910. [From _Omar E. Pol_, Jun 21 2009]
%K nonn
%O 1,3
%A _Omar E. Pol_, May 02 2009, May 21 2010
%E More terms from _Omar E. Pol_, Jun 16 2009
%E Extended by _R. J. Mathar_, Feb 05 2010
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