

A141104


Lower Even Swappage of Upper Wythoff Sequence.


4



2, 4, 6, 10, 12, 14, 18, 20, 22, 26, 28, 30, 34, 36, 38, 40, 44, 46, 48, 52, 54, 56, 60, 62, 64, 68, 70, 72, 74, 78, 80, 82, 86, 88, 90, 94, 96, 98, 102, 104, 106, 108, 112, 114, 116, 120, 122, 124, 128, 130, 132, 136, 138, 140, 142, 146, 148, 150, 154, 156, 158, 162
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OFFSET

1,1


COMMENTS

This question has an affirmative answer, as proved by Russo and Schwiebert in the link below. It can also be proved using the Walnut theoremprover, using synchronized Fibonacci automata for the two sequences. These automata take n and y as input, in Fibonacci (Zeckendorf) representation, and accept iff y = a(n) for the respective sequence.  Jeffrey Shallit, Jan 27 2024


LINKS



FORMULA

Let a = (1,3,4,6,8,9,11,12,...) = A000201 = lower Wythoff sequence; let b = (2,5,7,10,13,15,18,...) = A001950 = upper Wythoff sequence. For each odd b(n), let a(m) be the least number in a such that after swapping b(n) and a(m), the resulting new a and b are both increasing. A141104 is the sequence obtained by thus swapping all odds out of A001950.


EXAMPLE

Start with
a = (1,3,4,6,8,9,11,12,...) and b = (2,5,7,10,13,15,18,...).
After first swap,
a = (1,3,5,6,8,9,11,12,...) and b = (2,4,7,10,13,15,18,...).
After 2nd swap,
a = (1,3,5,7,8,9,11,12,...) and b = (2,4,6,10,13,15,18,...).


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



