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Search: id:A000708
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| A000708 |
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Number of quasi-alternating permutations of length n.
(Formerly M4188 N1745)
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+0
5
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| 1, 1, 0, 1, 6, 29, 150, 841, 5166, 34649, 252750, 1995181, 16962726, 154624469, 1505035350, 15583997521, 171082318686, 1985148989489, 24279125761950, 312193418011861, 4210755676649046, 59445878286889709, 876726137720576550
(list; graph; listen)
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OFFSET
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0,5
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REFERENCES
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E. Netto, Lehrbuch der Combinatorik. 2nd ed., Teubner, Leipzig, 1927, p. 113.
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 261.
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FORMULA
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a(n)=|A000111(n+1)-2*A000111(n)| . - Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Jan 13 2007
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MAPLE
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seq(i!*coeff(series(((tan(t)+sec(t))^2-4*(tan(t)+sec(t)))/2, t, 35), t, i), i=2..24);
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CROSSREFS
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Equals (1/2)*A001758. A diagonal of A008970.
Adjacent sequences: A000705 A000706 A000707 this_sequence A000709 A000710 A000711
Sequence in context: A125785 A108982 A059724 this_sequence A027248 A020090 A020036
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KEYWORD
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nonn
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AUTHOR
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njas
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EXTENSIONS
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More terms, Maple code from Barbara Haas Margolius (margolius(AT)math.csuohio.edu) 3/12/01
Corrected and extended by T. D. Noe (noe(AT)sspectra.com), Oct 25 2006
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