If a sentence starts with a number, should it be spelt out in letters?

[morningpaper]

I am writing a report and using the convention of using digits for numbers over ten but should I start a sentence with a number or spell it out?

I would spell it out, unless it's 412,987. Or thereabouts.

I think it would look odd either way so I'd try and avoid it

thanks chaps, will go with bof

I think you should be consistent - but I thought it was digits for numbers over twelve (?)

At the start if a sentence, definitely write the number out in words, and I think the convention for numbers over 10 depends on the purpose/tone of the document - it makes me cringe if I'm reading a book (fiction) and a number appears. But for non-fiction, newspapers, formal docs - yes, numbers over ten in the body of the document would be digits.

I'm trying to think in what context you'd start a sentence, in a formal document, with a number? Other than 'Fifteen years ago, the defendant was....'

"Twenty participants start the blah blah"

(yes 'tis a report)

Yes, definitely not '20 participants' unless you were setting out a summary/bullet points.