OFFSET
1,1
COMMENTS
Conjecture: -2 < n*r - a(n) < 3 for n >= 1, where r = 1 + sqrt(3).
From Michel Dekking, Feb 27 2021: (Start)
The formula a(n) = 2*A026363(n) follows from the two facts that (a(n)) gives the positions of 1 in A284751, fixed point of the morphism mu given by
mu: 0 -> 01, 1 -> 0001,
and A026363 gives the positions of 1 in the fixed point of the morphism tau given by
tau: 0->11, 1 -> 101.
The non-overlapping words of length 2 occurring in (a(n)) at odd positions are a:=00 and b:=01. Their occurrences can be read from the fixed point of the morphism nu induced by mu, and are given by
nu: a =00 -> 0101 = bb, b =01 -> 010001 = bab.
The fact that tau is obtained under the alphabet change {a,b} -> {0,1} proves that (a(n)) is twice the sequence of occurrences of 1 in the fixed point of tau.
Interestingly, the conjecture: -2 < n*(1+sqrt(3))- a(n) < 3 , implies a conjecture: -1 < n*(1 + sqrt(3))/2 - A026363(n) < 3/2, which is stronger than the conjecture -1 < n*(1 + sqrt(3))/2 - a(n) < 2 given in the comments of A026363.
The best bounds are not simple to obtain, but the fact that (n*(1+sqrt(3))- a(n)) is a bounded sequence follows by a general symbolic discrepancy result, Theorem 1 in Adamscewski's 2004 paper. To apply that theorem, one writes a(n) as a sum of differences 1 and 2, corresponding to the words 1 and 10 in the fixed point 10111101... of tau. The induced morphism is given by 1->21, 2->2111, with eigenvalues of its incidence matrix 1+sqrt(3) and 1-sqrt(3). The boundedness result is then implied by the fact that the second eigenvalue is smaller than 1 in absolute value.
(End)
LINKS
Clark Kimberling, Table of n, a(n) for n = 1..10000
Boris Adamczewski, Symbolic discrepancy and self-similar dynamics, Annales de l'Institut Fourier 54 (2004), 2201-2234.
FORMULA
a(n) = 2*A026363(n). - Michel Dekking, Feb 27 2021
EXAMPLE
As a word, A284751 = 010001..., in which 1 is in positions 2,6,...
MATHEMATICA
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Apr 13 2017
STATUS
approved