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Search: id:A000475
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| A000475 |
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Rencontres numbers: permutations with exactly 4 fixed points.
(Formerly M4969 N2132)
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+0
10
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| 1, 0, 15, 70, 630, 5544, 55650, 611820, 7342335, 95449640, 1336295961, 20044438050, 320711010620, 5452087178160, 98137569209940, 1864613814984984, 37292276299704525, 783137802293789040, 17229031650463366195, 396267727960657413630
(list; graph; listen)
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OFFSET
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4,3
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REFERENCES
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J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 65.
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FORMULA
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a(n)=sum((-1)^j*n!/(4!*j!), j=2..n-4).
a(n) = A000166(n)*binomial(n+3, 3). - Robert Goodhand (robert(AT)rgoodhand.fsnet.co.uk), Nov 08, 2001
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MAPLE
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a:=n->sum(n!*sum((-1)^k/(k-3)!, j=0..n), k=3..n): seq(-a(n)/4!, n=3..22); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), May 25 2007
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CROSSREFS
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Cf. A000240, A000387, A000449.
A diagonal of A008291.
Sequence in context: A124893 A126402 A053134 this_sequence A126274 A053531 A000476
Adjacent sequences: A000472 A000473 A000474 this_sequence A000476 A000477 A000478
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KEYWORD
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nonn
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AUTHOR
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njas
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