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%I #6 Feb 07 2018 13:21:55
%S 0,1,0,1,1,0,2,1,1,1,2,2,0,1,2,3,1,2,1,2,1,2,2,3,2,3,0,1,1,2,2,3,3,4,
%T 1,2,2,3,1,2,2,3,1,2,2,3,2,3,3,4,2,3,3,4,0,1,1,2,1,2,2,3,2,3,3,4,3,4,
%U 4,5,1,2,2,3,2,3,3,4,1,2,2,3,2,3,3,4
%N Number of 3's in the n-th {2,3}-power tower; see Comments.
%C Suppose that S is a set of real numbers. As S-power-tower, t, is a number t = x(1)^x(2)^...^x(k), where k >= 1 and x(i) is in S for i = 1..k. We represent t by (x(1),x(2),...,x(k), which for k > 1 is defined as (x(1),((x(2),...,x(k-1)); (2,3,2) means 2^9. The number k is the *height* of t. If every element of S exceeds 1 and all the power towers are ranked in increasing order, the position of each in the resulting sequence is its *rank*. See A299229 for a guide to related sequences.
%C Every nonnegative integer occurs infinitely many times in the sequence. In particular, a(n) = 0 when the tower consists exclusively of 2's. The position of the n-th 0 in the sequence is the rank of the n-th {2}-power tower, given by 7*2^(n-3) - 1 for n > 2.
%H Clark Kimberling, <a href="/A299236/b299236.txt">Table of n, a(n) for n = 1..10000</a>
%e t(13) = (2,2,2,2), so that a(13) = 0.
%t t[1] = {2}; t[2] = {3}; t[3] = {2, 2}; t[4] = {2, 3}; t[5] = {3, 2};
%t t[6] = {2, 2, 2}; t[7] = {3, 3}; t[8] = {3, 2, 2}; t[9] = {2, 2, 3};
%t t[10] = {2, 3, 2}; t[11] = {3, 2, 3}; t[12] = {3, 3, 2};
%t z = 190; g[k_] := If[EvenQ[k], {2}, {3}]; f = 6;
%t While[f < 13, n = f; While[n < z, p = 1;
%t While[p < 12, m = 2 n + 1; v = t[n]; k = 0;
%t While[k < 2^p, t[m + k] = Join[g[k], t[n + Floor[k/2]]]; k = k + 1];
%t p = p + 1; n = m]]; f = f + 1]
%t Table[Count[t[n], 2], {n, 1, 100}]; (* A299235 *)
%t Table[Count[t[n], 3], {n, 1, 100}]; (* A299236 *)
%Y Cf. A299229, A299235 (complement).
%K nonn,easy
%O 1,7
%A _Clark Kimberling_, Feb 06 2018
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