The following example replicates a # character five times in front of a Student Number in the Students table:
SELECT [Student Name]
, REPLICATE('#', 5) + [Student Number] AS 'Student Number'
FROM [Students]
GO
Here is an example result set.
Student Name Student Number
Test Name 1 - #####STU1
Test Name 2 - #####STU2
Test Name 3 - #####STU3
Test Name 4 - #####STU4
Test Name 5 - #####STU5