9 999 999 in words is read as nine million, nine hundred and ninety-nine thousand, and nine hundred and ninety-nine
By partitioning, we can write 9 999 999 as follow
9 000 000 + 900 000 + 90 000 + 9000 + 900 + 90 + 9
If we start at the first digit of '9' on the left, the next digit is ten times smaller than the previous one.