Write following expressions in Python: a⁻ⁿ = 1 / aⁿ

int('a') produces error but following expression having int('a') in it, does not return error. Why?
len('a') + 2 or int('a')

\dfrac{a^n}{a^m} = a^{n - m}

(a^n)^m = a^{nm}