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#10 by N. J. A. Sloane at Mon Jul 30 00:44:18 EDT 2012
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#9 by Robert Price at Sun Jul 29 21:13:21 EDT 2012
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#8 by Robert Price at Sun Jul 29 21:12:43 EDT 2012
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| DATA
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1, 2, 4, 10, 22, 62, 176, 478436
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| EXTENSIONS
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a(7) corrected by Robert Price, Jul 29 2012
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| STATUS
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approved
editing
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#7 by Russ Cox at Sat Mar 31 10:32:24 EDT 2012
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| AUTHOR
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N. J. A. Sloane and _Jon Wild (wild(AT)music.mcgill.ca), _, Nov 24 2002
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Discussion
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| Sat Mar 31
| 10:32
| OEIS Server: https://oeis.org/edit/global/772
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#6 by Russ Cox at Fri Mar 30 16:49:32 EDT 2012
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| AUTHOR
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_N. J. A. Sloane (njas(AT)research.att.com) _ and Jon Wild (wild(AT)music.mcgill.ca), Nov 24 2002
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Discussion
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| Fri Mar 30
| 16:49
| OEIS Server: https://oeis.org/edit/global/110
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#5 by N. J. A. Sloane at Thu Nov 11 07:34:06 EST 2010
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| LINKS
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Jon Wild, <a href="="/A076875/a076875.gif">Illustration of a(4) = 22</a> (ignore the arrowheads)
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| KEYWORD
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nonn,nice,new
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#4 by N. J. A. Sloane at Fri Feb 27 03:00:00 EST 2009
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| LINKS
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Jon Wild, <a href="http://www.research.att.com/~njas/sequences/a076875.gif">Illustration of a(4) = 22</a> (ignore the arrowheads)
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| EXAMPLE
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See illustration for a(4)=22: each of the 12 solutions shown crosses the x-axis first, and ten of them are related by mirror symmetry to a corresponding curve that crosses the y-axis first, making the total a(4)=22.
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| KEYWORD
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nonn,nice,new
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| AUTHOR
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N. J. A. Sloane (njas (AT)research.att.com) and Jon Wild (wild(AT)music.mcgill.ca), Nov 24 2002
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#3 by N. J. A. Sloane at Tue Jul 19 03:00:00 EDT 2005
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| KEYWORD
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nonn,nice,new
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| AUTHOR
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njas and Jon Wild (wild(AT)fasmusic.harvardmcgill.educa), Nov 24 2002
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#2 by N. J. A. Sloane at Sat Sep 13 03:00:00 EDT 2003
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| DATA
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1, 2, 4, 10, 22, 62, 146176, 416478
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| KEYWORD
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nonn,nice,new
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| EXTENSIONS
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a(6) and a(7) corrected Aug 23 2003
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#1 by N. J. A. Sloane at Fri May 16 03:00:00 EDT 2003
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| NAME
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Meandric numbers for a curve crossing two perpendicular lines at n points.
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| DATA
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1, 2, 4, 10, 22, 62, 146, 416
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| OFFSET
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0,2
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| COMMENTS
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a(n) = number of ways that a curve can start in the (-,-) quadrant, cross the x and y axes at exactly n points and end in any quadrant. Line is undirected.
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| LINKS
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Jon Wild, <a href="http://www.research.att.com/~njas/sequences/a076875.gif">Illustration of a(4) = 22</a> (ignore the arrowheads)
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| FORMULA
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For n odd a(n) = 2*A076906(n).
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| EXAMPLE
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See illustration for a(4)=22: each of the 12 solutions shown crosses the x-axis first, and ten of them are related by mirror symmetry to a corresponding curve that crosses the y-axis first, making the total a(4)=22.
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| CROSSREFS
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Cf. A005316, A076876, A076906, A076907 (directed case).
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| KEYWORD
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nonn,nice
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| AUTHOR
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njas and Jon Wild (wild(AT)fas.harvard.edu), Nov 24 2002
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| STATUS
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approved
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