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%I #11 Jul 18 2019 11:39:06
%S 1,6,64,734,9276,124872,1753074,25366334,375677659,5667202856,
%T 86775157140,1345153548200,21069043965984,332927798516620,
%U 5301031234085664,84967018635587774,1369846562874360887,22199151535757780226,361411377745122110422,5908312923795257322184
%N (1/7) times the number of n-member subsets of [7n] whose elements sum to a multiple of n.
%C Also (1/6) times the number of n-member subsets of [7n-1] whose elements sum to a multiple of n.
%H Alois P. Heinz, <a href="/A309186/b309186.txt">Table of n, a(n) for n = 1..806</a>
%F a(n) = 1/(7n) * Sum_{d|n} binomial(7d,d)*(-1)^(n+d)*phi(n/d).
%p with(numtheory):
%p a:= n-> add(binomial(7*d, d)*(-1)^(n+d)*
%p phi(n/d), d in divisors(n))/(7*n):
%p seq(a(n), n=1..25);
%o (PARI) a(n) = 1/(7*n) * sumdiv(n, d, binomial(7*d,d)*(-1)^(n+d)*eulerphi(n/d)); \\ _Michel Marcus_, Jul 18 2019
%Y Column k=7 of A309148.
%K nonn
%O 1,2
%A _Alois P. Heinz_, Jul 15 2019
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