Process: Odd items, that is, the first, third and fifth items are 12,10,8. Then the seventh item (the first bracket) should be 6.

Even terms, that is, the second, fourth and sixth terms are 7, 6 and 5 respectively, then the eighth term (second bracket) should be 4.

Remarks: There are too many possibilities to find a pattern. Ask me if you have any questions ~