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Search: id:A000492
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| A000492 |
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Number of permutations of an n-sequence discordant with three given permutations (see reference) in n-6 places.
(Formerly M5092 N2204)
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+0
7
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| 20, 154, 1676, 14292, 155690, 1731708, 21264624, 280260864, 3970116255, 60113625680, 969368687752, 16588175089420, 300272980075896, 5733025551810600, 115148956467702600, 2427199940533198992, 53576182138937428377, 1235917889588345408586
(list; graph; listen)
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OFFSET
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6,1
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REFERENCES
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J. Riordan, Discordant permutations, Scripta Math., 20 (1954), 14-23.
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FORMULA
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a(n) = coefficient of y^6 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, 6), n=6..30); #code for f(n, k) is given in A000440
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CROSSREFS
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Cf. A000500, A000470, A000440, A000476, A000380, A000388.
Adjacent sequences: A000489 A000490 A000491 this_sequence A000493 A000494 A000495
Sequence in context: A100190 A022680 A108647 this_sequence A015866 A101091 A120693
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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, formula and Maple code from Barbara Haas Margolius (margolius(AT)math.csuohio.edu) 2/17/01
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