Hi...

DECLARE @MissingNumbers TABLE (N INT)

Declare @vMax int

INSERT INTO @MissingNumbers

VALUES (1),(2),(4),(5),(7),(8),(11),(12),(13),(15),(17),(19),(20)

Set @vMax = (Select MAX(N) from @MissingNumbers)

;with wcte as (

Select Top(@vMax) ROW_NUMBER() over(order by a.N) NAll

from @MissingNumbers a, @MissingNumbers b

) Select NAll from wcte a

Left outer Join @MissingNumbers b on b.N = a.Nall

where b.N is Null

Atif SHeikh