1. Write a recursive function to determine if a number is divisible by 3, without using % or loops.
2. Write a recursive function to print out the numbers from 1 to n, counting by 3's. Do not use loops.
3. Write a recursive function to print the numbers n to 1, counting by 2's 
4. Write a recursive function to print the numbers n to 1, counting by k's 
5. Write a recursive function to compute the n'th number in the following sequence:
    - the first number is 1
    - the second number is 2
    - the n'th number is the product of the previous two numbers
    for example, s(3) is 2, s(4) is 4, s(5) is 8, s(6) is 32...
6. Write a recursive function to compute the n'th number in the following sequence:
    - the first number is 2
    - the second number is 2
    - the n'th number is the difference of the previous two numbers, plus 2
7. Write a recursive function to compute the n'th number in the following sequence:
    - the first number is 1
    - the second number is 2
    - the third number is 2
    - the n'th number is the previous number times 3, minus 1.
8. Write a recursive function to compute the alternating sum 1-2+3-4+5-6+7-8...±n