Find missing numbers in a sequence

DECLARE @LowerLimit INT
DECLARE @UpperLimit INT
DECLARE @MissingNumberList VARCHAR(MAX)

SET @LowerLimit = 20
SET @UpperLimit = 25;

CREATE TABLE #Sample
(
    Number INT
)

INSERT INTO #Sample
SELECT 10 UNION ALL
SELECT 11 UNION ALL
SELECT 12 UNION ALL
SELECT 13 UNION ALL
SELECT 14 UNION ALL
SELECT 16 UNION ALL
SELECT 18 UNION ALL
SELECT 19 UNION ALL
SELECT 21 UNION ALL
SELECT 22 UNION ALL
SELECT 24 UNION ALL
SELECT 25 UNION ALL
SELECT 29 UNION ALL
SELECT 30 UNION ALL
SELECT 1 UNION ALL
SELECT 2 UNION ALL
SELECT 10;




WITH CTE AS
(
    SELECT @LowerLimit AS N
    UNION ALL
    SELECT N + 1 AS N
    FROM CTE WHERE N < @UpperLimit
)

--SELECT N AS MissingNumbers FROM CTE
--LEFT JOIN #Sample S ON CTE.N = S.Number
--WHERE S.Number IS NULL

SELECT @MissingNumberList = ISNULL(@MissingNumberList,'') + CAST(N AS VARCHAR) + ', ' FROM CTE
LEFT JOIN #Sample S ON CTE.N = S.Number
WHERE S.Number IS NULL

IF @MissingNumberList <> ''
SET @MissingNumberList = SUBSTRING(@MissingNumberList, 0, LEN(@MissingNumberList)-1)
SELECT @MissingNumberList AS MissingNumberList


DROP TABLE #Sample

create table test(numbers int)
 
insert into test values(1)
insert into test values(2)
insert into test values(3)
insert into test values(5)
insert into test values(6)
insert into test values(10)
insert into test values(11)

declare @num int
set @num=1
while @num <=(select max (numbers)from test)
begin
	if(@num = (select numbers from test where numbers=@num))
		begin
			print @num	
		end
	else
		begin 
			select @num 'Num'
		end
	set @num=@num +1
	
end