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A309184 (1/5) times the number of n-member subsets of [5n] whose elements sum to a multiple of n. 2
1, 4, 31, 244, 2126, 19780, 192130, 1922740, 19692535, 205444504, 2175519380, 23322657460, 252631900236, 2760767859784, 30400169157656, 336977765092788, 3757141504436393, 42107201575818028, 474084628585822413, 5359833704140818744, 60823006052351729266 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also (1/4) times the number of n-member subsets of [5n-1] whose elements sum to a multiple of n.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..925

FORMULA

a(n) = 1/(5n) * Sum_{d|n} binomial(5d,d)*(-1)^(n+d)*phi(n/d).

MAPLE

with(numtheory):

a:= n-> add(binomial(5*d, d)*(-1)^(n+d)*

        phi(n/d), d in divisors(n))/(5*n):

seq(a(n), n=1..25);

CROSSREFS

Column k=5 of A309148.

Sequence in context: A183911 A039765 A001091 * A077615 A039306 A265949

Adjacent sequences:  A309181 A309182 A309183 * A309185 A309186 A309187

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Jul 15 2019

STATUS

approved

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Last modified September 23 15:23 EDT 2021. Contains 347618 sequences. (Running on oeis4.)