This tweet contains exactly four As, one B, three Cs…
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There's more in the thread than just the curiosity.
I wrote a program in Lisp way back when that reproduces this kind of sentence, and allowed you to begin and end with any phrase bits you wish (eg: You might find it highly unlikely, but I can tell you that this sentence actually contains..., commas and a single exclamation mark to finish it off!) It was ugly but it worked. And thankfully didn't take 22 days since some word combinations did indeed lead to a fail.
I think it might have actually been Hofstadter's writing, and this exercise specifically, that got me interested in Lisp in the first place.