T-SQL Code to backup database with multiple files - Syntax error

Hello,

I'm trying to backup a database into multiple files but I'm getting a syntax error.

Here is the code:

declare @DBName varchar(100)
declare @DBFileName varchar(256)
declare @FolderName varchar(256)
declare @Path varchar(100)

set @Path = '\\Backup-Server\Test\'
set @DBName = 'DayNite'

set @DBFileName = 'DayNite-Full' + '-' + (SELECT CONVERT(char(10), GetDate(),110)) + '-' + 'P'
set @FolderName =(SELECT CONVERT(char(10), GetDate(),110))
set @Path = @Path + @FolderName + '\'


EXEC master.dbo.xp_create_subdir @Path

--Calculate broken files  for BACKUP DATBASE Function
/*declare @dbsize int
set @dbsize = (SELECT ((size*8)/1024)/1000 as SizeGB FROM sys.database_files WHERE file_id = '1')
set @dbsize = @dbsize / 4
print @dbsize*/

EXEC
BACKUP DATABASE [test] TO
DISK = @Path + @DBFileName + '1.bak',
DISK = @Path + @DBFileName + '2.bak',
DISK = @Path + @DBFileName + '3.bak',
DISK = @Path + @DBFileName + '4.bak',
DISK = @Path + @DBFileName + '5.bak',
DISK = @Path + @DBFileName + '6.bak',
DISK = @Path + @DBFileName + '7.bak',
DISK = @Path + @DBFileName + '8.bak',
DISK = @Path + @DBFileName + '9.bak',
DISK = @Path + @DBFileName + '10.bak',
DISK = @Path + @DBFileName + '11.bak',
DISK = @Path + @DBFileName + '12.bak',
DISK = @Path + @DBFileName + '13.bak'
WITH INIT , NOUNLOAD , NAME = 'DayNite Full Backup', NOSKIP , NOFORMAT