A concert hall has the following numbers of seats in the first 5 rows. . 18 seats in row 1
• 21 seats in row 2
• 24 seats in row 3
• 27 seats in row 4
• 30 seats in row 5
As the row number increases, the number of seats continues to follow the same pattern, resulting in an arithmetic
sequence. Which explicit formula gives the terms of this sequence?