Common Lisp algorithms -- 2

Write a function that counts and returns the number of each nucleotide in the given string sequence regardless of whether it's uppercase or lowercase. Write a function that computes the ratio of Guanine and Adenosine in the sequence. Using function PRIME? defined above, write function that takes a positive prime number n as a parameter, and returns the smallest prime greater than n. See unit test below for examples of what this function returns.