1, number reasoning 5 / 3, 5 / 4, 10 / 8, (), 13 / 12, answer and rule 2, number reasoning 124361251020, (), answer is 71428, find the rule

1, number reasoning 5 / 3, 5 / 4, 10 / 8, (), 13 / 12, answer and rule 2, number reasoning 124361251020, (), answer is 71428, find the rule

Is there an option for question one?
2、 12436125102071428 when you see this kind of question, you should think of the ten and the hundred of each item separately
124 ,1,2,4
3612, 3, 6, 12 are arithmetic sequences
51020 5,10,20
71428 7,14,28