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A246611
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Number of endofunctions on [n] whose cycle lengths are multiples of 4.
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2
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1, 0, 0, 0, 6, 120, 2160, 41160, 866460, 20294064, 526680000, 15036999120, 468848156040, 15859299473160, 578619457031616, 22654279249875000, 947570269816868880, 42174922731482980320, 1990416896317283627520, 99290011292792071612704, 5220362654145754082460000
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OFFSET
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0,5
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LINKS
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FORMULA
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a(n) ~ n^(n-3/8) * sqrt(Pi) / (2^(1/8) * GAMMA(1/8)) * (1 - 11 * sqrt(2/n) * GAMMA(1/8) / (64 * GAMMA(5/8))). - Vaclav Kotesovec, Sep 01 2014
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MAPLE
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with(combinat):
b:= proc(n, i) option remember; `if`(n=0, 1,
`if`(i>n, 0, add(b(n-i*j, i+4)*(i-1)!^j*
multinomial(n, n-i*j, i$j)/j!, j=0..n/i)))
end:
a:= a->add(b(j, 4)*n^(n-j)*binomial(n-1, j-1), j=0..n):
seq(a(n), n=0..20);
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MATHEMATICA
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CoefficientList[Series[1/(1-LambertW[-x]^4)^(1/4), {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Sep 01 2014 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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