Sam is collecting pennies. On the first day of the month, Samnis given 16 pennies. Each day after that he gets 4 more pennies. Which of the following equations defines how many pennies he has after the nth day?

A. an = 16n + 4
B. an = 4n + 16
C. an = 4n + 16
D. an = 64n - 64​