In Tara's math class, each student made up a number pattern for classmates to identify. These are the numbers that Tara wrote. Find the pattern and identify the first and seventh numbers in the table.
a. first number:
b. seventh number:
Tara's Pattern
1st
2nd
3rd
4th
5th
6th
7th
3/8
5/16
9/32
17/64
33/128