Тогда
lim [(n+1)^2/(3n+3)(3n+2)(3n+1)(3n)!]/[(3n)!/n^2]
lim (n+1)^2/[3(n+1)(3n+2)(3n+1)n^2]
lim (n+1)/[3(3n+2)(3n+1)n^2