Prove the following using mathematical induction:
1. (ab)n = an bn for every natural number n
2. 13 +23+33+…+n3 = (1+2+3+…+n)2
3. 1+3+5+7+…+(2n-1) = n2
Consider an array of prime integers in the range [1...20] with the entries randomly distributed. Find the average number of comparisons for a sequential search in the array.