OFFSET
0,2
LINKS
Marko Riedel et al., Number of n-element subsets divisible by n
FORMULA
a(n) = (-1)^n * (1/n) * Sum_{d|n} C(4d,d)*(-1)^d*phi(n/d) for n>0, a(0)=1.
MAPLE
with(numtheory); a := n -> `if`(n=0, 1, (-1)^n * 1/n * add(binomial(4*d, d)*(-1)^d*phi(n/d), d in divisors(n)));
PROG
(PARI) a(n) = if (n, (-1)^n * (1/n) * sumdiv(n, d, binomial(4*d, d)*(-1)^d*eulerphi(n/d)), 1); \\ Michel Marcus, Aug 27 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Marko Riedel, Aug 26 2018
STATUS
approved