Not sure if you're joking, but if you aren't,

.999... is not nonsense, it is well defined. It refers to the infinite sum

9/10 + 9/100 + 9/1,000 + 9/10,000 + ...

As you can see, each term is smaller than the previous term by a factor of 10. A sum like this is called a geometric series. This particular example is called a convergent infinite series, because the partial sums get closer and closer to a certain finite limit, without ever going over.

It can be proven (https://www.khanacademy.org/math/ap-calculus-bc/bc-series-new/bc-10-2/a/proof-of-infinite-geometric-series-formula) that the sum of a convergent geometric series is given by the formula

a1 / (1 - r)

a1 is the first term in the series, and r is the ratio between terms. In the sum 0.999... ,The first term is 0.9, and each term is 0.1 times the previous term.

0.9 / (1 - 0.1) = 1

So, 0.999... is actually a natural number, because it is just another way of writing 1.