What combinations of letters don’t appear together in the english language? English is a pretty open language that has accepted and taken on many words from many different languages, as opposed to a language like french which is state controlled and has strict rules about new words. This openness means that there are surprising few combinations that don’t appear and they nearly all revolve around the letter Q.
So what are they?
JQ, QG, QK, QY, QZ, WQ and WZ.
This is handy to know if you want to use a placeholder in text that you want to find and replace easily later without replacing letters in actual words. It’s also extremely helpful if you are using letter frequency to break a cipher.
English letter frequency counts – Peter Norvig
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More frequency analysis