A sequence of pentagonal numbers is started below.

1. Find the next three pentagonal numbers.

   Answer (a):

   $13, 17, 21$What kind of sequence do the pentagonal numbers form?

2. What is the equation for the n^th pentagonal number?

   Hint (b):

   Is a constant being added to each number to obtain the next? Multiplied? Neither?

3. What is the equation for the $n^{th}$ pentagonal number?

   Answer (c):

   $t\left(n\right) = 4n − 3$