To put this in everyday context, imagine you are standing in the pasta aisle of a grocery store with someone who double-majored in Computer Science and Mathematics, minored in Physics and you went as far as high school Algebra II. You have a splitting headache and all you want to do is stock up on a variety of pasta. After a quick perusal of prices, you start tossing eight or ten packages into your shopping cart. You are already thinking about the next thing on the list when the other person asks, "What is the meaning of pasta numbers?"
What I answered at the time was, "I have no idea; I choose by shape, price, and what I plan to cook."
Apparently, there is some confusion even on the internet regarding this question and the correct answer. Shocking, I know.
On one website where authentic Italian chefs answer questions such as this, I found one answer:
"Dear iliene, you are right about the different type of pasta but, the different n° are exiting only for the spaghetti (the real king of the italian pasta!) The rule is: bigger is the number (i.e.: spaghetti n° 7) and bigger will be the diameter of the single spaghetto (and the way you will taste it under yout teeth)...the spaghetti n° 5 are smaller than spaghetti n° 7."
Not willing to settle for such an incomprehensible answer, I checked good old Wikipedia under Pasta. If you're interested in etymology, evolution, or history, it's there. So are some photographs and blah, blah, blah about pasta in other countries, the only thing of interest to me was which countries produced and consumed the most pasta. Nothing about pasta numbers.
Undeterred, I clicked on one small link in the excessively long Wikipedia entry, which lead to Federal Requirements for Specific Standardized Macaroni and Noodle Products. I have much better things to do with my time, but I was curious and yes, really, OUR GOVERNMENT is controlling pasta. What would Cookie Monster do? I like to think he would shove cookies with both of his furry blue hands into his mouth, while screaming something politically incorrect.
We all use math every day. What I can tell you is that my Luigi Vitelli pasta, product of Italy, but manufactured for and distributed by Vitelli Foods LLC, Fair Lawn, New Jersey uses number 8 for spaghetti, number 9 for spaghettini, 27 for rigatoni, 86 for penne rigate and has no number for fettucine.