my $fail = qr/^     # Start looking at the begining of the string
	(?!             # and immediately fail if you find
			7000$   # "7000" then the end of the string 
                    # (ie. the whole string = "7000")
		| 	7777$   # or "7777"
		|	7778$   # etc.
		|	3886200$
		|	2200$
		|	8488$
		|	3406$
		|	9100$
		|	29389988$
		|	7688$
		|	5000$
		|	20$
		|	3408$
		|	3404$
		|	7648$
	)               # If you got this far with failing (ie. matching the enclosed.
	\d+$            # then match if the whole string consists of digits.
/x

##</code><code>##

my $fail = qr/^(?!(?:7000|7777|7778|3886200|2200|8488|3406|9100|29389988|7688|5000|20|3408|3404|7648)$)\d+$/;