The Crane Pool Forum

"23 skidoo (sometimes 23 skiddoo) is an American slang phrase generally
referring to leaving quickly, being forced to leave quickly by someone else,
or taking advantage of a propitious opportunity to leave. Popularized during
the early 20th century, the exact origin of the phrase is uncertain."

23 Skidoo (Phrase) Wikipedia Page

Charley bought some popcorn
Billy bought a car
Someone almost bought the farm,
but they didn't get that far.
Things shut down at midnight,
at least around here they do.
'Cause we all reside down the block inside
at 23 Skidoo. -- John Prine; Jesus, The Missing Years

I've long been aware of the Flatiron Building theory, but the one about A Tale of Two Cities is new to me. I kinda like it!

Apparently it has nothing to do with the number of pairs of human chromosomes.