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Search: id:A109034
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| 1, 0, 1, 4, 16, 66, 280, 1216, 5384, 24224, 110464, 509480, 2372704, 11142656, 52709600, 250933120, 1201354240, 5780413760, 27937867520, 135574988800, 660314620160, 3226731934720, 15815752724480, 77735943378560
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OFFSET
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0,4
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REFERENCES
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Ian Le, Wilf classes of pairs of permutations of length 4, The Electronic J. of Combinatorics, 12, 2005, R25.
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FORMULA
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G.f.=[1-sqrt(1-8x+16x^2-8x^3)]/[4x]
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MAPLE
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G:=(1-sqrt(1-8*x+16*x^2-8*x^3))/4/x: Gser:=series(G, x=0, 30): 1, seq(coeff(Gser, x^n), n=1..27);
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CROSSREFS
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Cf. A109033.
Sequence in context: A026762 A082307 A099782 this_sequence A110276 A026883 A151242
Adjacent sequences: A109031 A109032 A109033 this_sequence A109035 A109036 A109037
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 16 2005
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