477823895domain: NAppears in sequencesa(n) = (-1)^(n+1)*Sum_{k=0..n+1}(-1)^k*binomial(2*k,k).at n=15A054108Expansion of x/((1-x)*sqrt(1+4*x^2)).at n=33A104551Expansion of x/((1-x)*sqrt(1+4*x^2)).at n=34A104551