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Search: id:A000500
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| A000500 |
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Number of permutations of an n-sequence discordant with three given permutations (see reference) in n-7 places.
(Formerly M5223 N2273)
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+0
7
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| 31, 304, 4230, 43880, 547338, 6924960, 94714620, 1375878816, 21273204330, 348919244768, 6056244249682, 110955673493568, 2140465858763844, 43379533256972640, 921616584567907176, 20485188316420940640, 475499882089797554181, 11506280235885243825696
(list; graph; listen)
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OFFSET
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7,1
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
J. Riordan, Discordant permutations, Scripta Math., 20 (1954), 14-23.
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FORMULA
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a(n) = coefficient of y^7 in sum_0^n sigma_{n, k}(n - k)!(y - 1)^k on y where the sigma_{n, k} have generating function sigma(t, u)=(1 - 2t^2(u^2) - 2t^2(1 + t)u^3 + 3t^4(u^4))(1 - tu)^( - 1)(1 - (1 + 2t)u - tu^2 + t^3(u^3))^( - 1).
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MAPLE
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seq(f(n, 7), n=7..30); #code for f(n, k) is given in A000440
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CROSSREFS
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Cf. A000492, A000470, A000440, A000476, A000380, A000388.
Sequence in context: A115151 A001298 A027841 this_sequence A141912 A147297 A002225
Adjacent sequences: A000497 A000498 A000499 this_sequence A000501 A000502 A000503
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms, formula and Maple code from Barbara Haas Margolius (margolius(AT)math.csuohio.edu) 2/17/01
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