In general, spell out numbers of one or two words or those that begin a sentence.
If a sentence begins with a number, spell out the number or rewrite the sentence.
Rewriting the sentence may be a better alternative, and it is often less awkward if the number is long.
When one number immediately follows another, spell out one and use figures for the other.
three 100-meter events
25 four-poster beds
Exercise: Numbers
Related topic:
Hyphens with fractions and compound numbers