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A217262
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Delta sequence for binary words in a minimal-change order (subset-lex Gray code).
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1
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0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 4, 1, 0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 2, 5, 2, 1, 0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 4, 1, 0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 2, 3, 6, 3, 2, 1, 0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 4, 1, 0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 2, 5, 2, 1, 0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 4, 1, 0, 1, 2, 1, 0, 3, 0, 1, 2, 1, 0, 1, 2, 3, 4
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OFFSET
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0,3
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COMMENTS
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Positions of change with a certain Gray code (SL-Gray) for binary words (see example): to keep the sequence independent of the word length we start with the all-ones word, the sequence gives the following changes. The Gray code is cyclic, so first words skipped can (for fixed word length) be appended to the end.
Alternatively, for words length n, start with the all-zeros word, use transitions (n-2), (n-1), (n-2), (n-3), (n-4), ..., 3, 2, 1, 0, followed by the terms of this sequence until all 2^n words have been visited (see rows 00..05 in the example).
The subset-lex Gray code shown here can be obtained by a reflection process from the (reversed) subset-lexicographic order for binary words given in A108918.
Research problem: Does a two-close Gray code exist for the binary words of length n for all n? One-close Gray codes for binary words exists for n<=6 but not for n=7 (and unlikely for any n>=8, see Fxtbook link).
From Joerg Arndt, Apr 29 2014: (Start)
Sequence can be obtained from A007814 by replacing 0 by 01210, 1 by 3, 2 by 141, 3 by 12521, 4 by 1236321, ..., n by 123..(n-1)(n+2)(n-1)..321. - Joerg Arndt, Apr 29 2014
The consecutive transitions are either one-close (abs(a(n)-a(n-1))=1, most of the time) or 3-close (abs(a(n)-a(n-1))=3): In the Gray code of the 2^n n-bit words all transitions are one-close but for 2^(n-2) - 2 transitions that are 3-close; The Gray codes for n<=3 have only one-close transitions.
(End)
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LINKS
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Joerg Arndt, Table of n, a(n) for n = 0..4095
Joerg Arndt, Matters Computational (The Fxtbook), section 20.3.2 "Adjacent changes (AC) Gray codes", p.400.
Joerg Arndt, C++ code to compute this sequence.
Joerg Arndt, Subset-lex: did we miss an order?, arXiv:1405.6503 [math.CO], (26-May-2014)
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EXAMPLE
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Example for word length 5:
no: word transition
00: ..... .1... 3
01: 1.... 1.... 4
02: 11... .1... 3
03: 111.. ..1.. 2
04: 1111. ...1. 1
05: 11111 ....1 0 <--= sequence starts
06: 111.1 ...1. 1
07: 11..1 ..1.. 2
08: 11.11 ...1. 1
09: 11.1. ....1 0
10: 1..1. .1... 3
11: 1..11 ....1 0
12: 1...1 ...1. 1
13: 1.1.1 ..1.. 2
14: 1.111 ...1. 1
15: 1.11. ....1 0
16: 1.1.. ...1. 1
17: ..1.. 1.... 4
18: ..11. ...1. 1
19: ..111 ....1 0
20: ..1.1 ...1. 1
21: ....1 ..1.. 2
22: ...11 ...1. 1
23: ...1. ....1 0
24: .1.1. .1... 3
25: .1.11 ....1 0
26: .1..1 ...1. 1
27: .11.1 ..1.. 2
28: .1111 ...1. 1
29: .111. ....1 0
30: .11.. ...1. 1
31: .1... ..1.. 2
Append first few words to obtain Gray code for word length 5:
00: ..... .1...
01: 1.... 1....
02: 11... .1...
03: 111.. ..1..
04: 1111. ...1.
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CROSSREFS
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Cf. A007814 (transitions for the binary reflected Gray code).
Sequence in context: A127373 A200123 A187616 * A260616 A284950 A308298
Adjacent sequences: A217259 A217260 A217261 * A217263 A217264 A217265
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KEYWORD
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nonn
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AUTHOR
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Joerg Arndt, Sep 29 2012
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EXTENSIONS
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Prepended a(0)=0, Joerg Arndt, Apr 29 2014
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STATUS
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approved
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