I had a situation where I was importing a hierarchical structure into an application where a seq number had to be unique within each hierarchical level and start at 110 (for ease of subsequent manual insertion). The data beforehand looked like this... 
Level Prod        Type  Component      Quantity     Seq
1   P00210005       R   NZ1500         57.90000000  120
1   P00210005       C   P00210005M     1.00000000   120
2   P00210005M      R   M/C Operation   20.00000000 110
2   P00210005M      C   P00210006      1.00000000   110
2   P00210005M      C   P00210007      1.00000000   110
I wanted the row_number() function to generate the new sequence numbers but adding 10 and then multiplying by 10 wasn't achievable as expected. To force the sequence of arithmetic functions you have to enclose the entire row_number(), and partition clause in brackets. You can only perform simple addition and substraction on the row_number() as such.
So, my solution for this problem was 
,10*(10+row_number() over (partition by Level order by Type desc, [Seq] asc)) [NewSeq]
Note the position of the brackets to allow the multiplication to occur after the addition.
Level Prod        Type  Component      Quantity     [Seq] [NewSeq]
1   P00210005       R   NZ1500        57.90000000   120   110
1   P00210005       C   P00210005M    1.00000000    120   120
2   P00210005M      R   M/C Operation 20.00000000   110   110
2   P00210005M      C   P00210006     1.00000000    110   120
2   P00210005M      C   P00210007     1.00000000    110   130