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A309189
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(1/10) times the number of n-member subsets of [10n] whose elements sum to a multiple of n.
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2
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1, 9, 136, 2289, 42376, 834336, 17125354, 362345361, 7847250409, 173103073384, 3875837737520, 87857163416064, 2012268157890524, 46497242493163450, 1082614775186919136, 25374686712458407441, 598217593341171422090, 14176230568946364963825
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OFFSET
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1,2
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COMMENTS
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Also (1/9) times the number of n-member subsets of [10n-1] whose elements sum to a multiple of n.
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LINKS
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FORMULA
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a(n) = 1/(10n) * Sum_{d|n} binomial(10d,d)*(-1)^(n+d)*phi(n/d).
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MAPLE
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with(numtheory):
a:= n-> add(binomial(10*d, d)*(-1)^(n+d)*
phi(n/d), d in divisors(n))/(10*n):
seq(a(n), n=1..25);
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PROG
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(PARI) a(n) = 1/(10*n) * sumdiv(n, d, binomial(10*d, d)*(-1)^(n+d)*eulerphi(n/d)); \\ Michel Marcus, Jul 20 2019
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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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