2. A natural number can be encoded as a unarv string, For instance, 5 the string of aaaaa. Therefore, we may treat a set of numbers as a language over a unary alphabet (that contains only one symbol, e.g., a). Write down the regular expression for the following sets of numbers: (1). all the n such that n mod 3 = 1, (2), all the n such that n mod 3 = 0 or n mod 4 2