script spdPerm
　　property permutations : missing value
end script

on run
　　–Test by MacBook Pro 2012 Retina Core i7 2.6GHz
　　–set theList to {"A", "T", "G", "C", "1"} –0.05 secs (5 digits) 120 items.
　　–set theList to {"A", "T", "G", "C", "1", "2"} –0.21secs (6 digits) 720 items.
　　set theList to {"A", "T", "G", "C", "1", "2", "3"} –1.44 secs (7 digits) 5,040 items.
　　–set theList to {"A", "T", "G", "C", "1", "2", "3", "4"} –11.54 secs (8 digits) 40,320 items.
　　–set theList to {"A", "T", "G", "C", "1", "2", "3", "4", "5"} –107.27 secs (9 digits) 362,880 items.
　　
　　set aRes to permute(theList) of me
　　return length of aRes
end run

on permute(theList as list)
　　set theArray to current application’s NSMutableArray’s arrayWithArray:theList
　　set (permutations of spdPerm) to current application’s NSMutableArray’s array()
　　prmt(theArray, 0, (count theList) – 1)
　　
　　–Return AppleScript string list
　　set aFinishArray to current application’s NSMutableArray’s new()
　　set anEnum to (permutations of spdPerm)’s objectEnumerator()
　　repeat
　　　　set aValue to anEnum’s nextObject()
　　　　if aValue = missing value then exit repeat
　　　　set aStr to aValue’s componentsJoinedByString:""
　　　　(aFinishArray’s addObject:aStr)
　　end repeat
　　
　　return aFinishArray as list
end permute