8786123349domain: NAppears in sequencesa(n) = Sum_{k=0..floor(n/2)} binomial(n+4*k,n-2*k).at n=21A373904Expansion of (1 + x)/(1 - x^2*(1 + x)^4).at n=31A375316Expansion of (1 + x - x^3)/((1 + x - x^3)^2 - 4*x).at n=30A376785