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A046721 Number of semi-meanders of order n with 2 components. 2
1, 2, 6, 16, 48, 140, 428, 1308, 4072, 12796, 40432, 129432, 413900, 1342580, 4335288, 14201804, 46226896, 152594276, 500016036, 1660630740, 5472190206, 18264517264, 60475691308, 202684618564, 673892675030, 2266436498400, 7562707682032, 25510762766704, 85394319699916 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

LINKS

Andrew Howroyd, Table of n, a(n) for n = 2..40

P. Di Francesco, O. Golinelli and E. Guitter, Meander, folding and arch statistics, arXiv:hep-th/9506030, 1995.

CROSSREFS

Cf. A000682, A046726.

Sequence in context: A045694 A225178 A129772 * A230929 A291189 A214843

Adjacent sequences:  A046718 A046719 A046720 * A046722 A046723 A046724

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

EXTENSIONS

a(15)-a(30) from Andrew Howroyd, Nov 27 2015

STATUS

approved

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Last modified February 22 23:03 EST 2019. Contains 320411 sequences. (Running on oeis4.)