Look at the numbers 1.3.5.7, which are 1, 9, 15 and 19 respectively.

The difference between the two is 8.64, and then it should be 2. . That is 19+2=2 1.

Look at 2468. Yes 1, 2,5, 10.

There should be a difference of 7 after the difference of 1.35. . That is 10+7= 17.

This kind of topic generally adopts separation to find the law.