931226954949domain: NAppears in sequencesG.f.: sqrt( (1-x - sqrt(1-14*x+x^2)) / (6*x*(1-14*x+x^2)) ).at n=11A245927a(n) = Sum_{k=0..floor(n/3)} (-1)^k * binomial(n,3*k)^2.at n=23A307158