A factor is a positive integer that divides evenly into a given number. For example, the factors of 8 are 1, 2, 4, and 8.

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

The factors of 64 are [1, 2, 4, 8, 16, 32, 64] and the factors of 28 are [1, 2, 4, 7, 14, 28]. They share 3 factors [1, 2, 4] making 4 the greatest factor 64 and 28 have in common.

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To divide fractions, invert the second fraction and then multiply:

\( \frac{3}{8} \) ÷ \( \frac{2}{5} \) = \( \frac{3}{8} \) x \( \frac{5}{2} \)

To multiply fractions, multiply the numerators together and then multiply the denominators together:

\( \frac{3}{8} \) x \( \frac{5}{2} \) = \( \frac{3 x 5}{8 x 2} \) = \( \frac{15}{16} \) = \(\frac{15}{16}\)