At the point in elementary school when we are finally allowed to use calculators we also learn another skill: writing with numbers. There are a handful of numbers that, especially when displayed on the digital screen of those basic calculators translate directly to letters. Other numbers can be used more liberally and offer some room of interpretation while some work better upside down. It is a skill that will get perfected during all those boring classes when you should instead be learning about some advanced math.
On the higher education this skill of writing with numbers is further enhanced with other non-alphanumeric characters. It's especially popular among computer related fields of study where it's called leet speak (or 1337).
One of the words in Finnish you can write with numbers is iso which means big, or isot which is plural for big. So that gets us 1507, which happens to be todays count of my streak.
By the way, I have never thought there is no plural adjectives in English. Sounds a bit weird now that I think of it compared to Finnish. Just one of the weirdnesses of our language.