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A261503
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Number of necklaces with n white beads and 9*n black beads.
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2
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1, 1, 10, 136, 2290, 42376, 834472, 17125354, 362345362, 7847250409, 173103115760, 3875837737520, 87857163416200, 2012268157890524, 46497242510288804, 1082614775186919136, 25374686712458407442, 598217593341171422090, 14176230568954212214234
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OFFSET
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0,3
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LINKS
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Eric Weisstein's World of Mathematics, Necklace
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FORMULA
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a(n) = 1/(10*n) * Sum_{d|n} C(10*n/d,n/d) * A000010(d) for n>0, a(0) = 1.
a(n) ~ 10^(10*n-1/2) / (sqrt(2*Pi) * 9^(9*n+1/2) * n^(3/2)). - Vaclav Kotesovec, Aug 22 2015
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MAPLE
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with(numtheory):
a:= n-> `if`(n=0, 1, add(binomial(10*n/d, n/d)
*phi(d), d=divisors(n))/(10*n)):
seq(a(n), n=0..25);
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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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