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A001926
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G.f.: (1+x)^2/[(1-x)^4(1-x-x^2)^3].
(Formerly M4628 N1978)
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1
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1, 9, 46, 177, 571, 1632, 4270, 10446, 24244, 53942, 115954, 242240, 494087, 987503, 1939634, 3753007, 7167461, 13532608, 25293964, 46856332, 86110792
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| From rook polynomials.
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REFERENCES
| J. Riordan, Discordant permutations, Scripta Math., 20 (1954), 14-23.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| S. Plouffe, Approximations de S\'{e}ries G\'{e}n\'{e}ratrices et Quelques Conjectures, Dissertation, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.
S. Plouffe, 1031 Generating Functions and Conjectures, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.
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MAPLE
| A001926:=-(1+z)**2/(z**2+z-1)**3/(z-1)**4; [Conjectured (correctly) by S. Plouffe in his 1992 dissertation.]
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CROSSREFS
| Second differences are in A002941.
Sequence in context: A201458 A034487 A035039 * A085385 A081193 A054140
Adjacent sequences: A001923 A001924 A001925 * A001927 A001928 A001929
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Apr 10 2009
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