0.5 1 / 3 0.25 0.2

0.5 1 / 3 0.25 0.2

5 = 1 / 2, 0.25 = 1 / 4, 0.2 = 1 / 5, the sequence can be transformed into 1 / 2, 1 / 3, 1 / 4, 1 / 5, the rule is
1/(n+1)