Eventual strict increase conjectures for sixfold Thue–Morse representations

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Let t=t0t1t2⋯{\bf t}=t_0t_1t_2\cdots be the Thue–Morse sequence. For j≥2j\geq 2, define

rj(n):=∣{(x1,…,xj):n=∑1≤i≤jxi and txi=0 for 1≤i≤j}∣r_j(n):=\left|\{(x_1,\ldots,x_j):n=\sum_{1\leq i\leq j}x_i\text{ and }t_{x_i}=0\text{ for }1\leq i\leq j\}\right|

and

sj(n):=∣{(x1,…,xj):n=∑1≤i≤jxi and txi=1 for 1≤i≤j}∣.s_j(n):=\left|\{(x_1,\ldots,x_j):n=\sum_{1\leq i\leq j}x_i\text{ and }t_{x_i}=1\text{ for }1\leq i\leq j\}\right|.

Sixfold strict increase conjectures. The sequences r6(n)r_6(n) and s6(n)s_6(n) satisfy

r6(n)<r6(n+1)for n≥37,r_6(n)<r_6(n+1)\qquad\text{for }n\geq 37,

and

s6(n)<s6(n+1)for n≥5.s_6(n)<s_6(n+1)\qquad\text{for }n\geq 5.

Numerical experiments suggest that both sequences are eventually strictly increasing; the conjectured thresholds are 3737 for r6r_6 and 55 for s6s_6.

References

Primary source

Jean-Paul Allouche and Jeffrey Shallit, “Additive Properties of the Evil and Odious Numbers and Similar Sequences”, arXiv:2112.13627 (2022).

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