I would generally understand "written-out number" to mean a number written in words and not in numerals. So "seven" instead of "7".
Many style guides suggest that numbers that are part of a sentence should be written out. So you should write
I have three sisters.
But you can use numerals for money, measurements, page references and mathematical expressions. Large exact numbers or long decimals and vulgar fractions can be written as numerals.
I have £20. See page 234. There have been 2,438,180 reported cases.
It is inconvenient to start a sentence with a numeral, since it can't be capitalised. You often are able to rephrase, or write out the number.
Five hundred metres from my house is a little cottage.
There is a little cottage 500 metres from my house.
The exact way of expressing a number varies according to dialect. Generally you split into groups of three and give each group as
"X hundred and Y"
five hundred and eighty-three million,
one hundred and twelve.
If the number is more than 1000 but the hundreds digit is zero you need an extra "and"
This is also a fairly common toy problem for learning computer programming. see https://stackoverflow.com/questions/19504350/how-to-convert-numbers-to-words-in-python
And you can generate infinite examples with python, in the dialect of your choice.