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Revision History for A000208 (Bold, blue-underlined text is an addition; faded, red-underlined text is a deletion.)

Showing entries 1-10 | older changes
Number of even sequences with period 2n.
(history; published version)
#39 by Michael De Vlieger at Sat Apr 30 12:18:31 EDT 2022
STATUS

reviewed

approved

#38 by Joerg Arndt at Sat Apr 30 11:15:20 EDT 2022
STATUS

proposed

reviewed

#37 by Jon E. Schoenfield at Sat Apr 30 10:42:32 EDT 2022
STATUS

editing

proposed

#36 by Jon E. Schoenfield at Sat Apr 30 10:41:55 EDT 2022
COMMENTS

These are binary sequences (sequences of 1's and 0's), and two sequences are considered the same if one can be transformed into the other by translation and/or exchanging 1 and 0. A periodic sequence can be represented by enclosing one period in parentheses (for example , (00011011)). Even sequences contain an even number of 1's and an even number of 0's. - Michael B. Porter, Dec 22 2019

FORMULA

a(n) = (A000013(2*n) + A000013(n))/2 if n is even, A000013(2*n)/2 if n is odd. - _Randall L. Rathbun, _, Jan 11 2002

EXTENSIONS

More terms from _Randall L. Rathbun, _, Jan 11 2002

STATUS

approved

editing

#35 by Alois P. Heinz at Wed Jan 15 11:12:45 EST 2020
STATUS

reviewed

approved

#34 by Joerg Arndt at Wed Jan 15 10:34:23 EST 2020
STATUS

proposed

reviewed

#33 by Michael B. Porter at Sun Dec 22 21:30:50 EST 2019
STATUS

editing

proposed

Discussion
Wed Jan 15
10:34
Joerg Arndt: One could mention the word "necklace" as well.
#32 by Michael B. Porter at Sun Dec 22 21:29:22 EST 2019
EXAMPLE

For n=2, the sequences of length 2n=4 are (0000), (0001), (0011), and (0101). The other 12 possibilities are equivalent - for example, the sequence (1001) is a translation of (0011), and the sequence (1101) is equivalent to (0001) by exchanging 1's and 0's and then translating. Three Since three of these have an even number of 1's, so a(2) = 3. - Michael B. Porter, Dec 22 2019

#31 by Michael B. Porter at Sun Dec 22 21:27:58 EST 2019
COMMENTS

These are binary sequences (sequences of 1's and 0's), and two sequences are considered the same if one can be transformed into the other by translation and/or exchanging 1 and 0. A periodic sequence can be represented by enclosing one period in parentheses (for example (00011011)). Even sequences contain an even number of 1's and an even number of 0's. - Michael B. Porter, Dec 22 2019

EXAMPLE

For n=2, the sequences of length 2n=4 are (0000), (0001), (0011), and (0101). The other 12 possibilities are equivalent - for example, the sequence (1001) is a translation of (0011), and the sequence (1101) is equivalent to (0001) by exchanging 1's and 0's and then translating. Three of these have an even number of 1's, so a(2) = 3. - Michael B. Porter, Dec 22 2019

STATUS

approved

editing

#30 by Bruno Berselli at Fri Apr 18 02:38:54 EDT 2014
STATUS

proposed

approved