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%I #6 Feb 24 2021 02:48:19
%S 1,1,6,21,6,21,81,81,6,21,81,81,81,306,486,261,6,21,81,81,81,306,486,
%T 261,81,306,486,486,1161,2376,2241,801,6,21,81,81,81,306,486,261,81,
%U 306,486,486,1161,2376,2241,801,81,306,486,486,1161,2376,2241,1026,1161,2376,2916
%N a(0) = 1, a(1) = 1; a(2^i + j) = 3a(j) + 3a(j + 1) for 0 <= j < 2^i.
%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>
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Jan 02 2010