The topic is the cross arrangement of two groups of numbers. Numbers in odd positions are a rule, and numbers in even positions are also a rule.

The specific rules are as follows:

Numbers in odd positions: 1 () 3 () 5 () .......

The law is obvious. Add 2 to this odd-numbered digit to get the next odd-numbered digit.

Even Numbers: () 10 () 8 () 6 ........

The rule is: subtract 2 from the number on this even number to get the number on the next even number.

Original title: 1 10 3 8 5 6 (7) (4) (9).