lim_{n → ∞} a_n = +∞ The sequence a_n tend to +∞, if for every number A there exists number M such that, all terms a_n with index n * M are greater than A. The sequence a_n tend to +∞, if for all A can find such number M that infinity amount of termsa_{M+1}, a_{M+2}, ... are greater than A. Less than A there are finite amount of terms a_1, a_2, a_3, ... , a_M. That is always for any big A. lim_{n → ∞} a_n = -∞ The sequence a_n tend to -∞, if for every number A there exists number M such that, all terms a_n with index n * M are less than A. The sequence a_n tend to -∞, if for all A can find such number M that infinity amount of terms a_{M+1}, a_{M+2}, ... are less than A. Greater than A there are finite amount of terms a_1, a_2, a_3, ... , a_M. That is always for any small A.