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Search: id:A130268
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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
1
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| 1, 1, 4, 86, 2696, 168232, 15948032, 2172623168, 398846422144, 97541017510784, 29909993927387648, 11447388459863715328, 5284740632299379566592, 2927671399386587378671616
(list; graph; listen)
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OFFSET
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0,3
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FORMULA
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E.g.f.: Product_{k>0} cosh(x^k/k).
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EXAMPLE
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a(2)=4 because we have (1)(2)(3)(4), (12)(34), (13)(24), and (14)(23).
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MAPLE
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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
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Cf. A055922, A130219, A130220.
Sequence in context: A055776 A055591 A055764 this_sequence A116320 A122209 A059577
Adjacent sequences: A130265 A130266 A130267 this_sequence A130269 A130270 A130271
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)Eunet.yu), Aug 06 2007
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 24 2007
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