The equation for this sequence is:

a_n = a_n-1 + 2(n - 1)

where n is the term's order in the sequence, a_n is the value of the term, and a_n-1 is the value of the term before a_n. This makes the next number:

a₆ = a₅ + 2(6 - 1)
a₆ = 21 + 2(5)
a₆ = 31

If 64% of the town's 19,000 voters cast ballots the number of votes cast is:

(\( \frac{64}{100} \)) x 19,000 = \( \frac{1,216,000}{100} \) = 12,160

The mayor got 60% of the votes cast which is:

(\( \frac{60}{100} \)) x 12,160 = \( \frac{729,600}{100} \) = 7,296 votes.

To find the average of these 4 numbers add them together then divide by 4:

\( \frac{17 + 11 + 16 + 12}{4} \) = \( \frac{56}{4} \) = 14

The factors of a number are all positive integers that divide evenly into the number. The factors of 28 are 1, 2, 4, 7, 14, 28.

The commutative property states that, when adding or multiplying numbers, the order in which they're added or multiplied does not matter. For example, 3 + 4 and 4 + 3 give the same result, as do 3 x 4 and 4 x 3.