Crossword Genius

What may be read as 221? (5,3,2,1,4)

Ross

I believe the answer is:

three men in a boat

I'm a little stuck... Click here to teach me more about this clue!

'what may be' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'as 221?' is the wordplay.
I cannot quite see how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is found within the answer.
This explanation may well be incorrect...

'read' acts as a link.

Can you help me to learn more?

(Other definitions for three men in a boat that I've seen before include "skipper and his two best mates?" , "Funny story" , "Work" , "Novel of Thames travellers (5,3,2,1,4)" , "Jerome K. Jerome book (5,3,2,1,4)" .)

I've seen this clue in The Guardian.
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