Increment in varchar data type

Create table  #temp
(
Id int identity(1001,1),
user_code as 'LE'+REPLICATE('0',6-Len(Id))+Convert(Varchar(10),Id)
)


INSERT INTO #temp DEFAULT VALUES
INSERT INTO #temp DEFAULT VALUES
INSERT INTO #temp DEFAULT VALUES

create table  Table1
(
Id int identity(1,1),
user_code as case  len(Id) when 1 then 'LE00100'+convert(varchar,ID)
when 2 then 'LE0010'+convert(varchar,ID)
when 2 then 'LE001'+convert(varchar,ID)
else 'LE'+convert(varchar,ID)
end
)

Test:
INSERT INTO Table1 DEFAULT VALUES;
INSERT INTO Table1 DEFAULT VALUES
INSERT INTO Table1 DEFAULT VALUES
INSERT INTO Table1 DEFAULT VALUES
INSERT INTO Table1 DEFAULT VALUES;

select *From Table1 

create sequence SQforLE
    as int
	start with 1
    increment by 1
;
go

create table SQTable(
	Id varchar(10) constraint DFSQforLE default 'LE'+replace(str((next value for SQforLE), 6), space(1), '0')
);

--insert default data
declare @cnt int; set @cnt=100;
while @cnt <> 0 begin
	insert into SQTable default values;
	set @cnt=@cnt-1;
end;

--get the result
select * from SQTable;

CREATE FUNCTION NextNumber()
RETURNS Char(8)
AS
BEGIN
declare @lastValue Char (8)
Declare @result Char (8)
set @lastvalue = (select max(custNumber) from Customers) 	
if @lastvalue is null 
set @lastvalue = 'LE001001' 
Declare @cnt integer
set @cnt = right(@lastvalue , 4) + 1 
select @result = 'LE00' + convert(varchar(8), @cnt) 	

RETURN @result
END