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A130268
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Number of degree-2n permutations such that number of cycles of size k is even (or zero) for every k.
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0
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1, 1, 4, 86, 2696, 168232, 15948032, 2172623168, 398846422144, 97541017510784, 29909993927387648, 11447388459863715328, 5284740632299379566592, 2927671399386587378671616
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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FORMULA
| E.g.f.: Product_{k>0} cosh(x^k/k).
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EXAMPLE
| a(2)=4 because we have (1)(2)(3)(4), (12)(34), (13)(24) and (14)(23).
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MAPLE
| g:=product(cosh(x^k/k), k=1..30): gser:=series(g, x=0, 30): seq(factorial(2*n)*coeff(gser, x, 2*n), n=0..13); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 24 2007
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CROSSREFS
| Cf. A055922, A130219, A130220.
Sequence in context: A055591 A055764 A163279 * A204460 A162086 A116320
Adjacent sequences: A130265 A130266 A130267 * A130269 A130270 A130271
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KEYWORD
| easy,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Aug 06 2007
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 24 2007
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