a(n) = (1/(4*n)) * Sum_{d|n} mu(n/d) * binomial(2*d, d)^2.
A028576
a(n) = (1/(4*n)) * Sum_{d|n} mu(n/d) * binomial(2*d, d)^2.
Terms
- a(0) =1a(1) =4a(2) =33a(3) =304a(4) =3175a(5) =35556a(6) =420665a(7) =5176000a(8) =65664000a(9) =853367900a(10) =11309870605a(11) =152342891952
External references
- oeis: A028576