generates rare usernames that are usually not taken by using the least used letters source: https://pi.math.cornell.edu/~mec/2003-2004/cryptography/subs/frequencies.html
here are 2 free working 4 letter usernames: @4FJQ @NJ1V now 5 letters: @BVEVO @ZXGKV @FJXJJ @_XBXZ @1VYZY @SQAKM @BXZVB @P_USB @J-YUY @HQZRK @XDCPU
