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A130219
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Number of partitions of 2n-set in which number of blocks of size k is even (or zero) for every k.
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6
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1, 1, 4, 56, 631, 15457, 582374, 18589286, 894499204, 51154344582, 3823359163826, 274722100927166, 25458967562911128, 2569179797929092506, 284554990016509385086
(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 ab|cd, ac|bd, ad|bc and a|b|c|d.
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MAPLE
| g:=product(cosh(x^k/factorial(k)), k=1..35): gser:=series(g, x=0, 32): seq(factorial(2*n)*coeff(gser, x, 2*n), n=0..14); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Sep 01 2007
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CROSSREFS
| Cf. A055922, A102759, A111723, A111724.
Sequence in context: A101540 A026740 A191466 * A111874 A078533 A009058
Adjacent sequences: A130216 A130217 A130218 * A130220 A130221 A130222
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KEYWORD
| easy,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Aug 04 2007, Aug 05 2007
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Sep 01 2007
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