Provide a simple way to initialise repeating characters in strings

Provide a simple way to intialise strings such as:

s: (20)"*"					;; string of 20 *s
s: "^[20] "					;; string of 20 " "
s: (50)""					;; an empty string with length of 50, size 51
s: "^[50]"					;; ditto