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A032106 Number of reversible strings with n black beads and n-1 white beads. String is not palindromic. 0
1, 1, 4, 16, 60, 226, 848, 3200, 12120, 46126, 176232, 675808, 2599688, 10028292, 38777664, 150266880, 583395120, 2268771670, 8836291640, 34461586016, 134564376232, 526024564572, 2058357329184 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..23.

C. G. Bower, Transforms (2)

Elizabeth Wilmer, Notes on Stephan's conjectures 72, 73 and 74

FORMULA

"BHK[ n ](2n)" (reversible, identity, unlabeled, n parts, 2n elements) transform of 1, 1, 1, 1...

a(2n) = 1/4 * [C(4n, 2n) - C(2n, n)], a(2n+1) = A034872(4n+2)-A034872(4n+1).

CROSSREFS

Sequence in context: A128650 A072335 A081161 * A269462 A047097 A051043

Adjacent sequences:  A032103 A032104 A032105 * A032107 A032108 A032109

KEYWORD

nonn

AUTHOR

Christian G. Bower

STATUS

approved

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Last modified February 19 22:04 EST 2018. Contains 299357 sequences. (Running on oeis4.)